Spatial prediction method, image decoding method, and image coding method

ABSTRACT

A spatial prediction method capable of reducing the complexity of spatial prediction includes: detecting an edge (E) overlapping the current block by obtaining a horizontal gradient (Gy) and a vertical gradient (Gx) between pixels within a block adjacent to the current block; calculating an integer slope of the edge; determining, for each pixel position within the current block, a sub-pel position being an intersection between (i) a line that has the integer slope and passes through the pixel position and (ii) a boundary of the adjacent block; and predicting, for each pixel position, a pixel value at the pixel position based on a pixel value interpolated in the sub-pel position, wherein the boundary of the adjacent block is a row or a column that is the closest to the current block, among rows or columns of pixels included in the adjacent block.

TECHNICAL FIELD

The present invention relates to a spatial prediction method in codingand decoding an image, and in particular to a directional spatialinterpolation involving edge detection or to efficient implementation ofsuch an interpolation.

BACKGROUND ART

Spatial prediction methods, that is, spatial interpolation have beenemployed in many applications. In particular, spatial interpolationforms an essential part of many image and video coding and processingapplications. In hybrid image or video coding algorithms, spatialprediction is typically employed for determining a prediction for animage block based on the pixels of already coded/decoded blocks. On theother hand, spatial interpolation may also be used as a part of postprocessing the decoded image or video signal, in particular for errorconcealment.

The majority of standardized video coding algorithms are based on hybridvideo coding. Hybrid video coding methods typically combine severaldifferent lossless and lossy compression schemes in order to achieve thedesired compression gain. Hybrid video coding is also the basis forITU-T standards (H.26x standards such as H.261 and H.263) as well asISO/IEC standards (MPEG-X standards such as MPEG-1, MPEG-2, and MPEG-4).The most recent and advanced video coding standard is currently thestandard denoted as H.264/MPEG-4 advanced video coding (AVC) which is aresult of standardization efforts by joint video team (JVT), a jointteam of ITU-T and ISO/IEC MPEG groups.

An image signal (input signal or input video signal) input to an encoder(image coding apparatus) is a sequence of images called frames (videoframes), each frame being a two-dimensional matrix of pixels. All theabove-mentioned standards based on hybrid video coding includesubdividing each individual frame into smaller blocks consisting of aplurality of pixels. Typically, a macroblock (usually denoting a blockof 16×16 pixels) is the basic image element, for which the coding isperformed. However, various particular coding steps may be performed forsmaller image elements, denoted subblocks or simply blocks and havingthe size of, for instance, 8×8, 4×4, and 16×8.

In the intra coding in accordance with H.264/MPEG-4 AVC, spatialprediction is performed on subblocks or macroblocks of the sizes of 8×8,4×4, 16×16 in order to reduce spatial redundancy. Spatial prediction isalso referred to as spatial interpolation, intra prediction, or intraframe prediction. Spatial prediction using a spatial direction isreferred to as directional spatial prediction. Furthermore, coding usingsuch spatial prediction is referred to as intra coding or spatialcoding, and an image or a block that is intra-coded is an intra-codedimage or an intra-coded block. Intra-frame prediction uses a predefinedset of intra-prediction modes (spatial prediction modes including thedirectional prediction mode), which basically predict the current(prediction target) block using the boundary pixels of the neighboringblocks already coded.

FIG. 1 schematically illustrates the eight directional spatialprediction modes used for the subblocks of 4×4 pixels. The differenttypes (modes) of directional spatial prediction refer to different edgedirections, i.e. the direction of the applied two-dimensionalextrapolation as illustrated in FIG. 1. There are eight differentdirectional prediction modes and one DC prediction mode for subblocks ofthe sizes 4×4 and 8×8, and three different directional prediction modesand one DC prediction mode for the macroblocks of 16×16 pixels.

Eight of the directional spatial prediction modes are labeled by a value302 of range {0, 1, 3, 4, 5, 6, 7, 8} and associated with predictions ineight different directions 301. The remaining one prediction mode(spatial prediction mode) is labeled by a value of 2 and called “DCprediction mode”. In the DC prediction mode, all pixels in a block arepredicted by a single value, which is the mean value of the surroundingreference pixels. In the eight directional spatial prediction modes, thecurrent block is predicted so that the reference pixels are repeatedalong the corresponding directions 301. For instance, the vertical modethat is a directional spatial prediction mode labeled with “0”vertically repeats the reference pixels of the row immediately above thecurrent block. The horizontal mode that is a directional spatialprediction mode labeled with “1” horizontally repeats the referencepixels of the column immediately to the left of the current block. Theremaining directional spatial prediction modes labeled with values from3 to 8 are diagonal intra prediction modes, according to which thereference pixels are diagonally repeated in the respective diagonaldirections.

In video coding, intra-coded blocks serve for refreshing the videosequence and stopping the error propagation. However, the efficiency ofthe spatial coding is lower than the performance of the temporal coding(inter coding), which leads to a lower overall compression gain as wellas to high variations of the resulting bit rate.

In order to increase the coding efficiency, an improved spatialprediction in which the number of extrapolation directions forpredicting pixels of a block is not limited to eight is suggested (seePTL 1). Rather, edge detection is performed within the already decodedneighboring blocks in PTL 1. Based on detection of the edge determinedas dominant, the pixels of the block are extrapolated or interpolatedpossibly from a sub-pel position between pixels belonging to aneighboring block.

PTL 1 enables a more precise determination of a prediction direction.This leads to a more precise spatial prediction, which, on the otherhand, results in smaller prediction error signal (difference between thecurrent block and a predicted block) and thus, to a better compression.

PATENT LITERATURE

-   [PTL 1] European Patent Application Publication No. 2081386

SUMMARY OF INVENTION Technical Problem

However, the edge detection and the extrapolation or interpolation inthe direction of the detected dominant edge require a plurality ofrather complex calculations such as divisions, which increases thecomplexity and reduces the easiness of implementation of the codingand/or decoding. In a lot of applications, it is necessary that at leastthe decoder (image decoding apparatus) has as low complexity aspossible. In particular, employment in devices with a limited powersupply and/or processing methods requires low-complexity implementationsof an encoder and/or a decoder.

The present invention has been conceived to solve the problems, and theaim of the present invention is to provide a spatial prediction methodthat can reduce complexity of the spatial prediction.

Solution to Problem

In order to achieve the aim, a spatial prediction method according to anaspect of the present invention is a spatial prediction method forspatially predicting a pixel value at each pixel position within acurrent block included in an image, and the method includes: detectingan edge that overlaps the current block by obtaining a horizontalgradient and a vertical gradient between pixels within a block adjacentto the current block; calculating an integer slope based on at least oneof the horizontal gradient and the vertical gradient, the integer slopeindicating an integer value of a slope of the detected edge; determininga sub-pel position for each of the pixel positions within the currentblock, the sub-pel position being an intersection between (i) a linethat has the calculated integer slope and passes through the pixelposition and (ii) a boundary of the adjacent block; and predicting, foreach of the pixel positions, the pixel value at the pixel position basedon a pixel value interpolated in the sub-pel position determined for thepixel position, wherein the boundary of the adjacent block is a row or acolumn that is closest to the current block, among a plurality of rowsor a plurality of columns of pixels included in the adjacent block.

Thereby, the integer slope of the edge that overlaps the current block(edge entering the current block) is first calculated, and the sub-pelposition corresponding to each of the pixel positions within the currentblock is determined according to the integer slope. Here, the sub-pelposition for each of the pixel positions within the current block can bedetermined using the integer slope, without a division. Thus, thedivision can be prevented for each of the pixel positions within thecurrent block. In other words, it is possible to prevent for each of thepixel positions within the current block (i) multiplication of thecoordinate value horizontal or the vertical to the pixel position, byone of the horizontal component and the vertical component of the edge,and (ii) division of the result of the multiplication by the other ofthe horizontal component and the vertical component. As a result, evenwhen calculation of the integer slope of the edge requires a divisiononly once, the division for each of the pixel positions within thecurrent block can be prevented, and the complexity of the spatialprediction can be reduced. In other words, complex operations can besuppressed.

In other words, the spatial prediction method according to an aspect ofthe present invention is characterized by calculating an integer slopeof the detected edge solely for the current block based on at least oneof a vertical gradient and a horizontal gradient, and determining anintersection of the line of the integer slope and a row or a column ofthe boundary pixels in the neighboring blocks.

Furthermore, in the calculating, the one of the horizontal gradient andthe vertical gradient may be scaled by a c-th power of 2, and theinteger slope may be calculated using the scaled one of the horizontalgradient and the vertical gradient, c being a positive integer, and inthe determining, the sub-pel position for the pixel position may becalculated by multiplying the integer slope generated by the scaling bya coordinate value horizontal or vertical to the pixel position to bepredicted within the current block.

Since the integer slope is calculated by scaling one of the verticalgradient and the horizontal gradient by a c-th power of 2, the precisionof the integer slope can be increased by the scaling when the integerslope is calculated by a division in which a value indicating a gradientto be scaled is used as the number to be divided (numerator).Furthermore, since scaling by a c-th power of 2 is performed, thescaling can be easily performed by shifting bits of the value to theleft. Furthermore, the sub-pel position calculated by this scaling canbe easily rescaled by shifting bits of the value to the right.Furthermore, since the precision of the integer slope is higher, theprecision of the sub-pel position can be increased.

The spatial prediction method may further include calculating the valueof c using a function of the one of the horizontal gradient and thevertical gradient.

Accordingly, the scaling using an appropriate c can be implemented. Forexample, the integer slope is calculated by a division in which thevalue indicating the gradient to be scaled is used as the number to bedivided (numerator). When the value is larger, overflow of the integerslope can be prevented by setting c to be applied to the gradientsmaller.

Furthermore, in the calculating, a result of a division may be obtainedwith reference to a division table stored in a memory, and the integerslope may be calculated using the obtained result of the division, thedivision using, as a divisor, a value indicating the one of thehorizontal gradient and the vertical gradient, and the division tableindicating, for each predetermined value, the predetermined value and aresult of a division using the predetermined value as a divisor.

Accordingly, since the division table indicating a result of thedivision in which a predetermined value is used as a divisor(denominator) for each of the values is referred to, the result can beeasily obtained without actually performing a division in which a valueindicating one of the horizontal gradient and the vertical gradient isused as a divisor (denominator). The integer slope can be calculatedusing the result of the division with ease, that is, with lowcomplexity.

Here, the memory may be either an internal memory or an external memoryof an apparatus that predicts a pixel value (intra prediction unit).Furthermore, in the result of the division indicated in the divisiontable, the number to be divided (numerator) is advantageously an a-thpower of 2, a being a positive integer. Still preferably, the value of ais a function of the horizontal or the vertical gradient, in particular,a function of the gradient applied as a divisor. This enables selectinghigher a for a larger divisor and lower a for a lower divisor, resultingin a further increase in the prediction accuracy.

Furthermore, a maximum value of the predetermined value indicated in thedivision table may be a b-th power of 2, b being an integer, and in thecalculating, when the value indicating the one of the horizontalgradient and the vertical gradient used as the divisor exceeds the b-thpower of 2, the one of the horizontal gradient and the vertical gradientmay be scaled by shifting bits of the value to the right to obtain theresult of the division using, as a divisor, a value indicating thescaled one of the horizontal gradient and the vertical gradient.

Accordingly, when a value indicating one of the horizontal gradient andthe vertical gradient as a divisor exceeds a b-th power of 2, that is,the maximum predetermined value indicated in the division table, thebits of the value indicating the gradient are shifted to the right, andthe result of the division using the value whose bits have been shiftedas a divisor is obtained from the division table. Thus, even withlimitation in the division table, the result of the division can beeasily obtained over the limit.

Furthermore, in the calculating, the integer slope may be calculated bydividing a value indicating one of the horizontal gradient and thevertical gradient by a value indicating the other of the horizontalgradient and the vertical gradient, when the pixel value at each of thepixel positions within the current block is predicted, weights may beset according to a distance, in the boundary, between the sub-pelposition determined for the pixel position and each of full-pelpositions adjacent to the sub-pel position, and the pixel value at thesub-pel position may be interpolated by setting a corresponding one ofthe weights to each pixel value of the full-pel positions andcalculating a weighted average of the pixel values.

Accordingly, the pixel value at the sub-pel position can beappropriately interpolated.

Furthermore, in the calculating, the integer slope may be calculatedsolely for the current block, and in the determining, the sub-pelposition may be determined for each of the pixel positions within thecurrent block, using the integer slope that is common to the pixelpositions.

Since one integer slope is calculated for the current block, thecomputation load can be suppressed.

The present invention can be implemented not only as such a spatialprediction method but also as an apparatus and an integrated circuiteach of which predicts a space by the spatial prediction method, as aprogram causing a computer to predict a space according to the spatialprediction method, and as a recording medium that stores the program.Furthermore, the present invention can be also implemented as an imagecoding apparatus and an integrated circuit each of which codes an imageusing the space predicted by the spatial prediction method, an imagecoding method for coding the image as such, a program causing a computerto code the image according to the image coding method, and a recordingmedium that stores the program. Furthermore, the present invention canbe also implemented as an image decoding apparatus and an integratedcircuit each of which decodes an image using the space predicted by thespatial prediction method, an image decoding method for decoding theimage as such, a program causing a computer to decode the imageaccording to the image decoding method, and a recording medium thatstores the program.

A spatial prediction device according to an aspect of the presentinvention is a spatial prediction device that spatially predicts a pixelvalue at each pixel position within a current block included in animage, and the device includes: a detection unit configured to detect anedge that overlaps the current block by obtaining a horizontal gradientand a vertical gradient between pixels within a block adjacent to thecurrent block; a calculation unit configured to calculate an integerslope based on at least one of the horizontal gradient and the verticalgradient, the integer slope indicating an integer value of a slope ofthe detected edge; a determining unit configured to determine a sub-pelposition for each of the pixel positions within the current block, thesub-pel position being an intersection between (i) a line that has thecalculated integer slope and passes through the pixel position and (ii)a boundary of the adjacent block; and a prediction unit configured topredict, for each of the pixel positions, the pixel value at the pixelposition based on a pixel value interpolated in the sub-pel positiondetermined for the pixel position, wherein the boundary of the adjacentblock is a row or a column that is closest to the current block, among aplurality of rows or a plurality of columns of pixels included in theadjacent block.

Furthermore, the calculation unit may be configured to scale the one ofthe horizontal gradient and the vertical gradient by a c-th power of 2,and calculate the integer slope using the scaled one of the horizontalgradient and the vertical gradient, c being a positive integer, and thedetermining unit may be configured to calculate the sub-pel position forthe pixel position by multiplying the integer slope generated by thescaling by a coordinate value horizontal or vertical to the pixelposition to be predicted within the current block.

The spatial prediction device may further include a coefficientcalculation unit configured to calculate the value of c using a functionof the one of the horizontal gradient (Gy) and the vertical gradient(Gx).

Furthermore, the calculation unit may be configured to obtain a resultof a division with reference to a division table stored in a memory, andcalculate the integer slope using the obtained result of the division,the division using, as a divisor, a value indicating the one of thehorizontal gradient (Gy) and the vertical gradient (Gx), and thedivision table indicating, for each predetermined value, thepredetermined value and a result of a division using the predeterminedvalue as a divisor.

Furthermore, a maximum value of the predetermined value indicated in thedivision table may be a b-th power of 2, b being an integer, and whenthe value indicating the one of the horizontal gradient (Gy) and thevertical gradient (Gx) used as the divisor exceeds the b-th power of 2,the calculation unit may be configured to scale the one of thehorizontal gradient and the vertical gradient by shifting bits of thevalue to the right to obtain the result of the division using, as adivisor, a value indicating the scaled one of the horizontal gradientand the vertical gradient.

Furthermore, the calculation unit may be configured to calculate theinteger slope by dividing a value indicating one of the horizontalgradient (Gy) and the vertical gradient (Gx) by a value indicating theother of the horizontal gradient and the vertical gradient, and theprediction unit may be configured to set weights according to adistance, in the boundary, between the sub-pel position determined forthe pixel position and each of full-pel positions adjacent to thesub-pel position, and interpolate the pixel value at the sub-pelposition by setting a corresponding one of the weights to each pixelvalue of the full-pel positions and calculating a weighted average ofthe pixel values.

Furthermore, the calculation unit may be configured to calculate theinteger slope solely for the current block, and the determining unit maybe configured to determine the sub-pel position for each of the pixelpositions within the current block, using the integer slope that iscommon to the pixel positions.

Advantageous Effects of Invention

The spatial prediction method according to the present invention canreduce the complexity of spatial prediction.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically illustrates eight directional prediction modes usedfor the subblocks of 4×4 pixels.

FIG. 2 is a block diagram of an image coding apparatus according toEmbodiment 1 of the present invention.

FIG. 3 is a block diagram of an image decoding apparatus according toEmbodiment 1.

FIG. 4A illustrates an edge vector and its projections into theorthogonal axes X and Y according to Embodiment 1.

FIG. 4B shows a raster of a 4×4 pixels of the block to be extrapolatedthat is a block to be predicted by extrapolation according to Embodiment1.

FIG. 4C illustrates an example in which an edge enters the block to bepredicted from the left side according to Embodiment 1.

FIG. 4D illustrates another example of an edge direction according toEmbodiment 1.

FIG. 5 is a flowchart indicating processes performed by the intraprediction unit according to Embodiment 1.

FIG. 6 is an example of a system according to Embodiment 1.

FIG. 7 is a flowchart indicating a spatial prediction method accordingto an aspect of the present invention.

FIG. 8 illustrates an overall configuration of a content providingsystem for implementing content distribution services.

FIG. 9 illustrates an overall configuration of a digital broadcastingsystem.

FIG. 10 illustrates a block diagram of an example of a configuration ofa television.

FIG. 11 is a block diagram illustrating an example of a configuration ofan information reproducing/recording unit that reads and writesinformation from or on a recording medium that is an optical disc.

FIG. 12 illustrates an example of a configuration of a recording mediumthat is an optical disc.

FIG. 13A illustrates an example of a cellular phone.

FIG. 13B illustrates a block diagram of an example of a configuration ofthe cellular phone.

FIG. 14 illustrates a structure of multiplexed data.

FIG. 15 schematically illustrates how each stream is multiplexed inmultiplexed data.

FIG. 16 illustrates how a video stream is stored in a stream of PESpackets in more detail.

FIG. 17 illustrates a structure of TS packets and source packets in themultiplexed data.

FIG. 18 illustrates a data structure of a PMT.

FIG. 19 illustrates an internal structure of multiplexed datainformation.

FIG. 20 illustrates an internal structure of stream attributeinformation.

FIG. 21 illustrates steps for identifying video data.

FIG. 22 illustrates a block diagram illustrating an example of aconfiguration of an integrated circuit for implementing the video codingmethod and the video decoding method according to each of Embodiments.

FIG. 23 illustrates a configuration for switching between drivingfrequencies.

FIG. 24 illustrates steps for identifying video data and switchingbetween driving frequencies.

FIG. 25 illustrates an example of a look-up table in which the standardsof video data are associated with the driving frequencies.

FIG. 26A illustrates an example of a configuration for sharing a moduleof a signal processing unit.

FIG. 26B illustrates another example of a configuration for sharing amodule of a signal processing unit.

DESCRIPTION OF EMBODIMENTS

Embodiments for implementing the present invention will be describedwith reference to drawings.

Embodiment 1

FIG. 2 is a block diagram illustrating an example of an encoder 100according to Embodiment 1. The encoder 100 includes a subtracting unit105, a transform quantization unit 110, an inverse quantization andinverse transform unit 120, an adding unit 125, a deblocking filter 130,a memory 140, an interpolation filter 150, a motion compensatedprediction unit 160, a motion estimation unit 165, an intra predictionunit 170, an intra/inter switch unit 175, a post filter design unit 180,and an entropy coding unit 190.

The subtracting unit 105 first determines differences (prediction errorsignal, residual signal, or prediction error block) between a currentblock to be coded of an input video signal (input signal) and acorresponding predicted block (prediction signal) predicted for thecurrent block. The prediction signal (predicted block) is obtainedeither by a temporal prediction (inter prediction) or by a spatialprediction. The type of prediction can be varied on a per frame basis,on a per slice basis, or on a per macroblock basis.

The predictive coding using the temporal prediction is referred to asinter coding, and the predictive coding using the spatial prediction isreferred to as intra coding. The type of prediction for a video framecan be set by the user or selected by the encoder 100 so as to achieve apossibly high compression gain. The intra/inter switch 175 provides acorresponding prediction signal to the subtractor 105 according to theselected prediction type. The prediction signal using temporalprediction is derived from the previously coded images which are storedin the memory 140. The prediction signal using spatial prediction isderived from the values of boundary pixels in the neighboring blocks ofthe same frame, which have been previously coded, decoded, and stored inthe memory 140. The memory 140 thus operates as a delay unit that allowsa comparison between current signal values (pixel values) to be codedand the prediction signal values (pixel values) generated from previoussignal values. The memory 140 can store a plurality of previously coded(and decoded) frames. The transform quantization unit 110 transforms thedifferences between the input signal and the prediction signal intocoefficients (frequency coefficients), and quantizes the differences.The differences are represented by a prediction error signal or aresidual signal. The entropy coding unit 190 performs entropy coding onthe quantized coefficients (coded video image or coded video sequence)in order to further reduce the amount of data in a lossless way. This ismainly achieved by applying a code to code words of variable lengthwherein the length of a code word is chosen based on the probability ofits occurrence. The entropy coding unit 190 outputs the coded signal(bitstream) including the entropy-coded video.

Intra-coded images (called also I-type images or I frames) consistsolely of macroblocks that are intra-coded, i.e. the intra-coded imagescan be decoded without reference to any other previously decoded image.The intra-coded images provide error resilience for the coded videosequence (coded video image) since they refresh the coded video sequencefrom errors possibly propagated from frame to frame due to temporalprediction. Moreover, I frames enable a random access within thesequence of coded video images.

The intra prediction unit 170 uses a predefined set of intra-predictionmodes. Some of the intra-prediction modes predict the current blockusing the boundary pixels of the neighboring blocks already coded. Otherintra-prediction modes, as template matching for example, use a searcharea made of already coded pixels belonging to the same frame.

The predefined set of intra-prediction modes includes some directionalspatial intra-prediction modes. The different modes of directionalintra-prediction refer to different directions of the appliedtwo-dimensional prediction. This allows efficient spatialintra-prediction in the case of various edge directions. The subtractor105 subtracts the prediction signal obtained by such an intra-predictionfrom the input signal as described above. Furthermore, the intraprediction unit 170 outputs intra-prediction mode information (not shownin FIG. 2) indicating the intra prediction mode to the entropy codingunit 190. The entropy coding unit 190 entropy-codes the intra-predictionmode information, and outputs the entropy-coded intra-prediction modeinformation together with the coded signal. The intra prediction unit170 according to Embodiment 1 further performs the distinctive spatialprediction aside from such processing. The distinctive spatialprediction will be described later.

Within the encoder 100, a decoding unit is incorporated for obtaining adecoded signal (local decoded signal). In other words, the encoder 100includes the inverse quantization and inverse transform 120 so that thedecoding is performed according to the coding processing. The inversequantization and inverse transform unit 120 performs inversequantization and inverse orthogonal transform (inverse frequencytransform) on the quantized value obtained by performing orthogonaltransform (frequency transform) and quantization on the prediction errorsignal. As a result, the inverse quantization and inverse transform unit120 generates and outputs a decoded prediction error signal.

The decoded prediction error signal differs from the original predictionerror signal due to the quantization error called also quantizationnoise. The adding unit 125 adds the decoded prediction error signal tothe prediction signal to obtain a reconstructed signal (reconstructedimage). In order to maintain the compatibility between the encoder 100(image coding apparatus) and the decoder (image decoding apparatus), theconstituent elements of the interpolation filter 150, the intraprediction unit 170, and the motion compensated prediction unit 160obtain the prediction signal based on the coded and subsequently decodedinput signal (decoded signal) which is known at both of the encoder 100and the decoder. Due to the quantization, quantization noise issuperposed to the reconstructed signal. Due to the block-wise coding,the superposed noise often has blocking characteristics, which results,in particular for strong quantization, in visible block boundaries inthe reconstructed image (image indicated by the reconstructed signal).In order to reduce these artifacts, the deblocking filter 130 performsdeblocking filtering on every reconstructed image block. The deblockingfilter 130 stores the reconstructed signal on which the deblockingfiltering has been performed, as a decoded signal in the memory 140.

In order to be decoded, the images coded by inter coding (inter-codedimages) require previously coded and subsequently decoded image (imageindicated by the decoded signal). Temporal prediction (inter prediction)may be performed uni-directionally, i.e., using only frames ordered intime before the current frame to be coded, or bi-directionally, i.e.,using also frames following the current frame. Uni-directional temporalprediction results in inter-coded images called P frames (P-pictures);and bi-directional temporal prediction results in inter-coded imagescalled B frames (B-pictures). In general, an inter-coded image may becomposed of any of P-, B-, or even I-type macroblocks. An inter-codedmacroblock (P- or B-macroblock) is predicted by employing the motioncompensated prediction unit 160. First, a best-matching block is foundfor the current block within the previously coded and decoded frames bythe motion estimation unit 165. Then, the motion compensated predictionunit 160 outputs the best-matching block as a prediction signal.Furthermore, the motion estimation unit 165 outputs, to the motioncompensated prediction unit 160, motion data that indicates relativedisplacement between the current block and its best-matching block andis data having the three-dimensional form (one temporal axis, twospatial axes) within the bitstream. In order to optimize the predictionaccuracy, the interpolation filter 150 transforms the resolution of areference image (decoded image) into a spatial sub-pel resolution e.g.half-pel or quarter-pel resolution. In other words, the interpolationfilter 150 interpolates sub-pixels in the reference image. Accordingly,the motion estimation unit 165 estimates a motion vector of sub-pelprecision.

The transform quantization unit 110 performs orthogonal transform(frequency transform) on and quantizes the prediction error signalindicating the differences between the current input signal and theprediction signal, in the intra- and the inter-coding modes, resultingin generation of the quantized value that is quantized coefficients(frequency coefficients). Generally, an orthogonal transform such as atwo-dimensional discrete cosine transform (DCT) or an integer versionthereof is employed since it reduces the correlation of the naturalvideo images efficiently. After the transform, low frequency componentsare usually more important for image quality than high frequencycomponents so that more bits can be spent for coding the low frequencycomponents than those of the high frequency components. The entropycoding unit 190 converts the two-dimensional matrix of the quantizedvalues into a one-dimensional array. Typically, this conversion isperformed by a so-called zig-zag scanning, which starts with theDC-coefficient in the upper left corner of the two-dimensional array andscans the two-dimensional array in a predetermined sequence ending withan AC coefficient in the lower right corner. As the energy is typicallyconcentrated in the upper left part of the two-dimensional matrix ofcoefficients, corresponding to the lower frequencies, the zig-zagscanning results in an array where usually the last values are zero.This allows for efficient coding using run-length codes as a partof/before the actual entropy coding.

Furthermore, the transform quantization unit 110 employs scalarquantization which can be controlled by a quantization parameter (QP)and a customizable quantization matrix (QM). The transform quantizationunit 110 selects one of 52 quantization parameters according to thecoefficients to be quantized, for each macroblock. In addition, aquantization matrix is specifically designed to keep certain frequenciesin the source to avoid losing image quality. Quantization matrix can beadapted to the coded video sequence and signalized together with thebitstream.

The bitstream (coded signal) includes two functional layers, a VideoCoding Layer (VCL) and a Network Abstraction Layer (NAL). The VCLprovides the coding functionality as briefly described above. The NALencapsulates information elements into standardized units called NALunits according to their further application such as transmission over achannel or storing in storage. The information elements are, forinstance, the coded prediction error signal (coded video image) or otherinformation necessary for the decoding of the coded video image (forexample, type of prediction, quantization parameter, and motionvectors). There are VCL NAL units containing the coded video image andthe related information, as well as non-VCL units encapsulatingadditional data such as parameter set relating to an entire coded videosequence, or Supplemental Enhancement Information (SEI) providingadditional information that can be used to improve the decodingperformance.

The post filter design unit 180 designs post filter information, such asfilter coefficients for improving the image quality, based on thedecoded signal and the input signal, and outputs the post filterinformation to the entropy coding unit 190. The post filter design unit180 sends the post filter information via SEI of the bitstream (SEImessage). In other words, the post filter design unit 180 compares thelocally decoded signal and the original input signal so that the encoder100 determines the post filter information. In general, the post filterinformation is information for allowing a decoder to set up anappropriate filter. The post filter information may be directly thefilter coefficients or another information enabling setting up thefilter coefficients. The post filter information, which is output by thepost filter design unit 180 is also fed to the entropy coding unit 190in order to be coded and inserted into the coded signal.

FIG. 3 is a block diagram illustrating an example of a decoder 200 thatis an image decoding apparatus according to Embodiment 1. The decoder200 is an apparatus that decodes a coded signal generated by the encoder100, and includes an inverse quantization and inverse transform unit220, an adding unit 225, a deblocking filter 230, a memory 240, aninterpolation filter 250, a motion compensated prediction unit 260, anintra prediction unit 270, an intra/inter switch 275, a post filter 280,and an entropy decoding unit 290. The inverse quantization and inversetransform unit 220, the adding unit 225, the deblocking filter 230, thememory 240, the interpolation filter 250, the motion compensatedprediction unit 260, the intra prediction unit 270, and the intra/interswitch 275 perform the same processing as the inverse quantization andinverse transform unit 120, the adding unit 125, the deblocking filter130, the memory 140, the interpolation filter 150, the motioncompensated prediction unit 160, the intra prediction unit 170, theintra/inter switch unit 175 that are included in the encoder 100,respectively.

More specifically, the entropy decoding unit 290 obtains a bitstreamthat is a coded signal (input signal to the decoder 200). The entropydecoding unit 290 entropy-decodes the quantized values (coded videoimage), the information elements necessary for decoding such as motiondata, mode of prediction etc., and the post filter information. Theentropy decoding unit 290 extracts, from the bitstream, theintra-prediction mode information indicating the type/mode of thespatial prediction applied to the block to be decoded as necessary. Theentropy decoding unit 290 outputs the extracted intra-prediction modeinformation to the intra prediction unit 270. The inverse quantizationand inverse transform unit 220 obtains the quantized values arranged ina one-dimensional array, and inversely scans the quantized values inorder to obtain a two-dimensional matrix. Furthermore, the inversequantization and inverse transform unit 220 performs inversequantization and inverse transform on the quantized values to obtain adecoded prediction error signal corresponding to a difference obtainedby subtracting the prediction signal from the input signal of theencoder 100.

The adding unit 225 obtains a prediction signal from either the motioncompensated prediction unit 260 or the intra prediction unit 270. Theintra/inter switch 275 switches between the temporal predictionperformed by the motion compensated prediction unit 260 and the spatialprediction performed by the intra prediction unit 270. In other words,prediction is switched according to switching information forsignalizing the prediction applied by the encoder 100. The switchinginformation further includes the information necessary for predicting(i) a prediction type in the case of intra-prediction (intra-predictionmode information), and (ii) motion data in the case of motioncompensated prediction. Depending on the current value of the motionvector, interpolation of pixel values may be needed in order to performthe motion compensated prediction. This interpolation is performed bythe interpolation filter 250. The adding unit 225 adds the decodedprediction error signal in the spatial domain to the prediction signalobtained either from the motion compensated prediction unit 260 or theintra prediction unit 270.

The deblocking filter 230 obtains the reconstructed image (reconstructedsignal) obtained by the adding, performs the deblocking filtering on theimage, and stores the resulting decoded signal in the memory 240. Thedecoded signal is applied to the temporal or spatial prediction of thefollowing blocks. The post filter 280 obtains the post filterinformation for setting up post filtering. The post filter 280 thenperforms the post filtering on the decoded signal in order to furtherimprove the image quality. Accordingly, the input signal that is thecoded signal is decoded, and the decoding result is output as an outputsignal.

The distinctive processing performed by the intra prediction units 170and 270 according to Embodiment 1 will be described in detail.

The problem underlying the present invention is based on the observationthat the efficiency of the spatial (intra) prediction applied to animage and video coding can be increased by improving the precision ofthe edge detection and subsequent prediction. On the other hand,improving the edge detection and prediction requires more computationalpower and applying more complex operations such as divisions. This maycause difficulties in efficiently implementing such more complexapproaches. For instance, employing only integer arithmetic for imageprocessing speeds up the coding and decoding and enables efficientimplementations on general purpose processors, digital signalprocessors, or in specialized or programmable hardware. However,depending on the precision of the integer, operations such asmultiplications and divisions may lead to overflows and/or decreasedprecision.

In order to increase the prediction performance of the intra-prediction,the intra prediction units 170 and 270 employ an improved intraprediction. In particular, the improved intra-prediction relies on edgedetection and calculates an intersection between a block boundary (or aplurality of them) and the edge detected as dominant. The intersectionmay be at a sub-pel position, and the interpolation is performed basedon such a sub-pel position. A corresponding example of intra-predictionmethod is disclosed, for instance, in PTL 1. The intra prediction units170 and 270 can more efficiently perform the directional spatialprediction with low-complexity in comparison with the intra-predictionmethod disclosed in PTL 1.

In general, edges in an image may be detected by determining a gradientvector field (gradient vector or gradient field) of the image (betweenpixels). A gradient vector is larger on an edge and is perpendicularthereto. One of the most popular approaches to detecting the gradientfield is convolution of the image with the vertical and horizontal Sobeloperators. The operators are expressed by the following masks (Equations1 and 2).

$\begin{matrix}\lbrack {{Math}\mspace{14mu} 1} \rbrack & \; \\{S_{x} = \begin{bmatrix}{- 1} & 0 & 1 \\{- 2} & 0 & 2 \\{- 1} & 0 & 1\end{bmatrix}} & ( {{Equation}\mspace{14mu} 1} ) \\\lbrack {{Math}\mspace{14mu} 2} \rbrack & \; \\{S_{y} = \begin{bmatrix}{- 1} & {- 2} & {- 1} \\0 & 0 & 0 \\1 & 2 & 1\end{bmatrix}} & ( {{Equation}\mspace{14mu} 2} )\end{matrix}$

In particular, a vertical gradient vector coordinate (verticalcoordinate or vertical gradient) Gx and a horizontal gradient vectorcoordinate (horizontal coordinate or horizontal gradient) Gy in aparticular pixel p(x,y) are then obtained by filtering the pixel p(x,y)with the vertical Sobel mask Sx and the horizontal Sobel mask Sy,respectively. Many applications employ a Sobel operator for obtainingthe gradient field. However, the present invention is not limited todetecting the gradient field by means of the Sobel operator. In general,any edge detection method that provides the gradient field may beemployed. For instance, masks with other sizes than the Sobel operatormay be used such as 2×2 or 4×4, or even larger masks may be used. Theselection of the particular mask depends on the desired results.Employing larger masks may add on precision of the edge detection andsuppress detection of small local edges, but on the other hand, itincreases the computational complexity. Alternatively, masks other thanthe Sobel mask may be used for edge detection, such as a Scharroperator, or operators based on higher derivatives.

After obtaining the vertical coordinate Gx and the horizontal coordinateGy of the gradient G, for a plurality of pixels of blocks surroundingthe block to be predicted, a dominant gradient or a dominant edge vectorcan be determined. A dominant edge vector (simply referred to as edge) Ewith the horizontal coordinate (horizontal components) Ex and thevertical coordinate (vertical components) Ey is perpendicular to thegradient vector G. Correspondingly, the sizes of the horizontalcomponents Ex and the vertical components Ey of the dominant edge vectorE correspond to the sizes of horizontal gradient Gy and verticalgradient Gx, respectively (for instance, Ex=−Gy, Ey=Gx for acounter-clock rotation). Typically, the dominant edge for the currentblock to be predicted is determined to be an edge with a maximum normout of edges (edges that overlap the current block) that intersect thecurrent block. However, other methods may be used as well, for instance,taking a weighted average of the edges, or the edge direction detectedfor a majority of pixels, etc.

It should be noted that the calculation of gradient is not necessarilyperformed for all pixels of the adjacent blocks (neighboring blocksadjacent to the current block to be predicted). In general, it isadvantageous to only calculate the gradient vector for pixels near theboundaries of the neighboring block adjacent to the block to beinterpolated (current block to be predicted). By calculating thegradient vector only for a subset of pixels in the adjacent block, thecomplexity is reduced. In particular, the rows and/or columns directlyadjacent to the current block are not well-suited for application of aSobel mask (or other gradient vector detecting masks) since the maskwould only partially overlap the adjacent block. Therefore, preferably,the second and/or third nearest row or column of pixels adjacent to thecurrent clock are used to calculate the gradient vector. However, thepresent invention is not limited thereto and other pixels in theadjacent block may be used as well.

Moreover, for the prediction, only the edges entering the block to bepredicted are of importance, thus edge detection near the boundariesalso reduces the risk of detecting a false edge.

FIG. 4A illustrates the edge vector E and its projections Ex and Ey(corresponding to gradients Gy and Gx, respectively) into the orthogonalaxes X and Y. FIG. 4B shows a raster of a 4×4 pixels of the block to beextrapolated (predicted). In particular, white circles and a blacksquare 440 represent pixels of the block to be extrapolated. The blacksquare 440 represents a current pixel p(x,y) whose value is to beextrapolated in an example below. Orthogonal axis X leads through abottom row of pixels belonging to a block adjacent to the block to bepredicted on its top side. The pixels of the row are illustrated asblack triangles or black circles. Orthogonal axis Y leads through anutmost right column of pixels belonging to a block adjacent to the blockto be predicted on its left side. The pixels of the column areillustrated as black circles.

An arrow 430 illustrates the edge detected as a dominant edge (dominantedge vector) E entering the block to be predicted. A dashed arrowillustratively extrapolates the dominant edge up to the current pixelp(x,y). The dominant edge E enters the block to be predicted at an angleα at a sub-pel 450 between two full-pels (integer pel) 410 and 420(illustrated as two black triangles). The sub-pel 450 needs to beinterpolated based on its distance to each of the two closest full-pels410 and 420.

In order to preserve the sharpness, position and direction of the edgeas far as possible, the current pixel 440 is extrapolated along the edgedirection based on the values of both of the full-pels 410 and 420.

[Math 3]

p(x,y)=w ₁ ·p(x−└δx┘,0)+w ₂ ·p(x−┌δx┐,0)  (Equation 3)

Here, w₁ and w₂ are weights, which are preferably determined based onthe distance from the intersection (sub-pel) 450 to each of thefull-pels 410 and 420. It is assumed that the point (0,0) lies near tothe top left corner of the block to be predicted. In Equation 3, thevalue multiplied by the weight w₁ of the first right side indicates thepixel value of the full-pel 420, and the value multiplied by the weightw₂ of the second right side indicates the pixel value of the full-pel410. Furthermore, δx indicates a positive value when an edge is along adirection from the upper left to the lower right as the edge 430 asillustrated in FIG. 4B. Furthermore, δx indicates a negative value whenan edge is along a direction from the upper right to the lower left. Forinstance, the weights w₁ and w₂ may be calculated as Equation 4 below.

[Math 4]

w ₁ =┌δx┐−δx

and

w ₂ =δx−└δx┘  (Equation 4)

Here, δx is distance between the X coordinate of the current pixel 440and the X coordinate of the intersection 450. The operator indicated byExpression 5 denotes the “floor” operation, which returns for a realoperand its nearest smaller integer (in this example equal to 1). Theoperator indicated by Expression 6 denotes the “ceil” operation, whichreturns for a real operand its nearest greater integer (in this exampleequal to 2).

[Math 5]

└·┘  (Expression 5)

[Math 6]

┌·┐  (Expression 6)

As can be seen in FIG. 4B, the slope k of the edge 430 may be calculatedas Equation 7 below.

$\begin{matrix}\lbrack {{Math}\mspace{14mu} 7} \rbrack & \; \\{k = {{\tan (\alpha)} = {\frac{Ey}{Ex} = \frac{y}{\delta \; x}}}} & ( {{Equation}\mspace{14mu} 7} )\end{matrix}$

Thus, the distance δx may be calculated as Equation 8 below.

$\begin{matrix}\lbrack {{Math}\mspace{14mu} 8} \rbrack & \; \\{{\delta \; x} = \frac{y \cdot {Ex}}{Ey}} & ( {{Equation}\mspace{14mu} 8} )\end{matrix}$

Thus, the calculation of δx requires a division. In general, for eachpixel of the block to be predicted, the distance δx from the Xcoordinate of the pixel to be predicted to the X coordinate of theintersection between the edge and the row of pixels of the topneighboring block (intersection to be interpolated between pixels in therow) is computed. Based on the calculated distance δx, then the currentpixel 440, that is, the pixel value of the current pixel 440 p(x,y) ispredicted as p(x,y)=p(x−δx,0), which means that the current pixel 440(the pixel value of the current pixel 440) is extrapolated as a value ofthe interpolated sub-pel 450.

According to Embodiment 1, all the above parameters are typicallyinteger values with a given precision and the operations applied areinteger operations. For instance, parameters Ex and Ey may berepresented by corresponding 8 bits long variables. In such a case, thedistance δx is also calculated using integer arithmetic by performing aninteger multiplication y×Ex and then by dividing the result by Ey. Ininteger arithmetic division, the result is also an integer, thus, theinteger division may slightly reduce the precision. In general, thereduction of precision gets higher for smaller values to be divided(y×Ex) and for greater values of a divisor (Ey).

In order to reduce the number of operations performed for predicting ablock of pixels as described above, the number of divisions to beperformed is reduced by calculating first the slope k of the edge Ewhich is common for all pixels of the block to be predicted. Thecalculated slope k is to be stored as an integer slope K=int(Ex/Ey) witha predefined precision. The computed integer slope K is then used tocalculate the distance δx for the current pixel to be predicted asEquation 9 below.

$\begin{matrix}\lbrack {{Math}\mspace{14mu} 9} \rbrack & \; \\{{\delta \; x} = {y \cdot {{int}( \frac{Ex}{Ey} )}}} & ( {{Equation}\mspace{14mu} 9} )\end{matrix}$

Here, the notation “int” emphasizes the fact that the operand is aninteger with a predefined precision. Accordingly, the division employedfor computing the slope is only performed once for the entire block ofpixels to be predicted. Moreover, since the Y coordinate of a pixel tobe predicted remains the same in the same row of pixels, the distance δxonly needs to be calculated once per row of pixels in the block to beinterpolated (predicted). The precision of the integer is typicallyselected according to the implementation environment. It may be, forinstance 8-bits, which is usual especially in image processing since theinput pixel components are also typically sampled with 8 bits. However,the precision may be also higher such as 12, 16, or any other number ofbits, or even lower than 8 bits.

However, performing the integer division Ex/Ey only once per block andthen obtaining row-wise the distance δx may lead to reduction of theprecision with respect to the solution in which the integermultiplication y×Ex is performed first and then the result is divided byEy. This is caused by the fact that the number Ex to be divided issmaller. Moreover, the subsequent multiplication of the integer slope bythe coordinate Y results in further multiplicative increase ofimprecision differently for different rows. In particular, the precisionwill be lower for higher values of y.

In order to further enhance the precision of the computation while stillkeeping the advantage of a single division per block, the integer slopeis obtained by multiplying the number to be divided by a scaling factor2^(c), as indicated by Equation 10, where c is an integer. δx_(block)denotes an integer slope obtained by multiplying a scaling factor.

$\begin{matrix}\lbrack {{Math}\mspace{14mu} 10} \rbrack & \; \\{{\delta \; x_{block}} = \frac{2^{c} \cdot {Ex}}{Ey}} & ( {{Equation}\mspace{14mu} 10} )\end{matrix}$

Advantageously, c is a positive integer. The value of c may be, forinstance, any value such as a value between 1 and 4. However, othervalues are also possible. The particular value may be selected takinginto account the block size. For instance, a possible value for c couldbe 4. The largest block size is 16×16, resulting in the highest value ofy being 16 (2⁴=16). Similarly, the value of c for blocks of size 4×4could be 2, and the value could be 3 for blocks of size 8×8. Thismultiplication is equivalent to shifting, to the left, c bits of thenumber Ex to be divided. This enlarges the value to be divided and,thus, the division by the divisor Ey will gain on precision. Thedistance δx can then be obtained as Equation 11 below.

[Math 11]

δx=y·δx _(block)  (Equation 11)

Here, the respective weights w₁ and w₂ can be calculated as Equations 12and 13 below.

[Math 12]

w ₁=(((δx+2^(c))>>c)<<c)−δx  (Equation 12)

[Math 13]

w ₂ =δx−((δx>>c)<<c)  (Equation 13)

Alternatively, the respective weights w1 and w2 can be calculated asEquations 14 and 15 below.

[Math 14]

w ₂ =δx&(2^(x)−1)  (Equation 14)

[Math 15]

w ₁=2^(c) −w ₂  (Equation 15)

Here, the operation “>>” denotes shifting c bits to the right, whichcorresponds to rescaling back by dividing the result by the appliedscaling factor 2^(c). The operation “<<” denotes shifting c bits to theleft, which corresponds to multiplying by the scaling factor 2^(c). Theoperation “&” denotes the bit-wise logical operator “AND”.

The values of δx and the weights w₁ and w₂ are non-shifted and arescaled by the factor 2^(c). The right shift to divide the final resultby the applied scaling factor 2^(c) must be done after interpolation ofthe sub-pel. In other words, the pixel value of the current pixel p(x,y)can be calculated as Equation 16 below.

[Math 16]

p(x,y)=(w ₁ ·p(x−(δx>>c),0)+w ₂·p(x−((δx+2^(c))>>c),0)+2^(c−1))>>c  (Equation 16)

Here, the offset 2^(c−1) serves for rounding the final value to thenearest integer. In the case where the precision of the value Ex hasbeen increased beforehand by multiplying it by 2^(p), p being an integer(6 is a good value), the increase of precision through the factor 2^(c)has for only purpose to divide by 2^(c) the error introduced through themultiplication by y. For example, the value of the integer slope isobtained by Equation 17 below.

$\begin{matrix}\lbrack {{Math}\mspace{14mu} 17} \rbrack & \; \\{{\delta \; x_{block}} = \frac{2^{c} \cdot ( {{Ex}{\operatorname{<<}p}} )}{Ey}} & ( {{Equation}\mspace{14mu} 17} )\end{matrix}$

Here, the distance δx can then be obtained as Equation 18 below. Theerror introduced through the division operation is multiplied by y/2^(c)and the distance δx is scaled by the factor 2^(p). The scaling isnecessary to calculate the distance in integer arithmetic while keepingthe possibility to have a sub-pel position for the intersection.

[Math 18]

δx=(y·δx _(block)+2^(c−1) >>c  (Equation 18)

The weights w₁ and w₂ can be obtained as Equations 19 and 20 below.

[Math 19]

w ₂ =δx&(2^(p)−1)  (Equation 19)

[Math 20]

w ₁=2^(p) −w ₂  (Equation 20)

The pixel value of the current pixel p(x,y) that is a prediction valuecan be calculated as Equation 21 below.

[Math 21]

p(x,y)=(w ₁ ·p(x−(δx>>p),0)+w ₂·p(x−((δx+2^(p))>>p),0)+2^(p-1))>>p  (Equation 21)

This calculation of the distance δx from the X coordinate of the currentpixel 440 to be predicted to the X coordinate of the intersection of theedge with the row of pixels adjacent to the block to be predicted on thetop enables increasing the precision of the division. However, due tomultiplication by y, the multiplications may result in rather highvalues, which, on the other hand, may cause an overflow, depending onthe integer precision supported by the computing environment.

In order to maintain the increased precision of the division whileavoiding the overflow, the scaling factor 2^(c) is selected according tothe value of the vertical gradient Gy, corresponding to the value of Exas indicated by Equation 22. According to Embodiment 1, each of theintra prediction units 170 and 270 may include a coefficient calculationunit that calculates c and the scaling factor 2^(c).

[Math 22]

c=f(Ex)  (Equation 22)

Here, function ƒ( ) is an arbitrary function. Advantageously, the valueof c is lower for higher values of Ex. One example for the function ƒ( )is expressed by Equation 23.

[Math 23]

c=8−int(log₂(|E _(x)|))  (Equation 23)

In such a case, c is equal to 8 for Ex equal to 1, c is equal to 1 forEx equal to 128, and c is equal to 0 for Ex equal to 256. If more bitsare available in the system, one could define the following function ofEquation 24 below.

[Math 24]

c=b−int(log₂(|E _(x)|))  (Equation 24)

Here, b is the maximum number of bits available in the system.Generally, the maximum possible precision should be used when Ex issmall (equal to 1 for example), and the maximum precision minus 8 bitsshould be used when Ex is big (close to 256). When calculating theparameter c, the sign of the edge vector coordinate Ex is not importantand thus c may, in general, also be calculated as c=f(|Ex|).

In accordance with another embodiment of the present invention, thedivision for calculating the integer slope of the edge is completelyavoided. This is facilitated by replacing the division with referring toa table (division table). Accordingly, a table is stored in a memory.The memory may be either an internal memory of the interpolationcomputing system (intra prediction unit) or an external memory. Thetable is composed of a limited number of divisors and a result ofdividing a predefined value. For instance, the table may include entrieswith a result of a division of a number 2^(a) by various values of Ey asindicated by Equation 25 below.

$\begin{matrix}\lbrack {{Math}\mspace{14mu} 25} \rbrack & \; \\{{{Table}\lbrack {{Ey}} \rbrack} = {{int}( \frac{2^{a}}{{Ey}} )}} & ( {{Equation}\mspace{14mu} 25} )\end{matrix}$

Here, a is a positive integer. For example, a can be equal to the valueof the precision p described previously. In order to perform processingusing the table instead of the division, preferably, the table divisionscaling factor 2^(a) is a function of the divisor size |Ey| as indicatedby Equation 26 below.

[Math 26]

a=g(|Ey|)  (Equation 26)

The function g( ) is an arbitrary function. Advantageously, the value ofthe scaling parameter a is higher for higher size (absolute value) ofEy. One example for the function g( ) is expressed by Equation 27.

[Math 27]

a=b+int(log₂(|E _(y)|))  (Equation 27)

Here, b is chosen so that the value b+8 does not overflow the number ofbits available in the system. Generally the maximum possible precisionshould be used for Ey that is big (close to 256) and a lower precisionshould be used for Ey that is small (close to 1). The above examples offunctions f( ) and g( ) are only for illustration. The values of thesefunctions may be either calculated on-the-fly or pre-stored in a tablein a memory. The functions f( ) and g( ) may also be given by a tablewithout referring to an analytic rule.

Then, the scaled integer slope may be obtained as Equation 28 below.

[Math 28]

δx _(block)=2^(c) ×Ex×Table[|Ey|]×sign(Ey)  (Equation 28)

Here, the operation “sign” returns a sign of the operand, and Table[ ]denotes a result of division by |Ey| retrieved from a look-up table in amemory. The distance δx can then be obtained similarly as previouslydescribed, that is, by Equation 29 below.

[Math 29]

δx=(y·δx _(block)+2^(c−1))>>c  (Equation 29)

In that case, the distance δx is scaled by a factor 2^(a). The values ofthe weights and a predictive pixel value of the pixel to be predictedcan be deduced from the previous equations by replacing p by a. Anotherpossibility is to keep the distance δx scaled by a factor 2^(c+a). Inthat case, the final prediction must be shifted to the right in order todivide the value by 2^(c+a). In other words, these processes can beexpressed by Equations 30 to 33.

[Math 30]

δx=y·δx _(block)  (Equation 30)

[Math 31]

w ₂ =δx&(2^(c+a)−1)  (Equation 31)

[Math 32]

w ₁=2^(c+a) −w ₂  (Equation 32)

[Math 33]

p(x,y)=(w ₁ ·p(x−(δx>>(c+a)),0)+w ₂·p(x−((δx+2^(c+a))>>(c+a)),0)+2^(c−1))>>(c+a)  (Equation 33)

In order to limit the memory requirements for storing the divisiontable, preferably only 2^(b) table entries are stored. This means that|Ey| entries only exist for 0<|Ey|≦2^(b). In other words, the maximumvalue of the divisors used for the division indicated in the divisiontable is 2^(b). Preferably, an entry (result of the division) is presentin the table for each value of Ey. However, this is not necessary forthe present invention and, in general, the table may list an entry onlyfor every second, or third of a value of Ey. If an entry is not present,the closest entry listed in the table is retrieved. However, listingonly some entries could result in a loss of accuracy.

If the divisor Ey is larger than the largest divisor listed in thetable, then, preferably the values of both edge vector coordinates Eyand Ex are shifted to the right by one bit, corresponding to division by2. In other words, the processes indicated by Equation 34 are performed.

$\begin{matrix}\lbrack {{Math}\mspace{14mu} 34} \rbrack & \; \\{( {{{Ey}} > 2^{b}} )\{ \begin{matrix}{{{Ex} = {Ex}}\operatorname{>>}1} \\{{{Ey} = {Ey}}\operatorname{>>}1}\end{matrix} } & ( {{Equation}\mspace{14mu} 34} )\end{matrix}$

After the shifting, the result of division is retrieved from the tablebased on the new value of the divisor Ey. If the result of division issuccessfully retrieved, the distance δx is calculated as shown above. Ifthe value of Ey is still too high, the shifting is repeated until aresult of division may be obtained. With this reduction of the number oftable entries, the resolution of the edge direction is slightlydecreased. However, advantageously, the memory requirements are limited.By setting the parameter b, a tradeoff between the edge directionresolution and memory requirements may be set appropriately for thegiven computing environment as well as for the size of the block to beinterpolated.

The above example has been described for the edge 430 entering from thetop side the block to be predicted.

FIG. 4C illustrates another example in which an edge 483 enters theblock to be predicted from the left side. In this example, thecalculation of a slope is also based on the determined gradients,however, the X and Y coordinates (and correspondingly, the Ex and Eycoordinates) are exchanged as indicated by Equations 35 and 36.

$\begin{matrix}\lbrack {{Math}\mspace{14mu} 35} \rbrack & \; \\{k_{1} = {\frac{Ey}{Ex} = \frac{\delta \; y_{1}}{x}}} & ( {{Equation}\mspace{14mu} 35} ) \\\lbrack {{Math}\mspace{14mu} 36} \rbrack & \; \\{{\delta \; y_{1}} = \frac{x \cdot {Ey}}{Ex}} & ( {{Equation}\mspace{14mu} 36} )\end{matrix}$

Consequently, the specific computations of the distance δy₁ will besimilar to those of δx in the previous example, however, the divisor nowis Ex rather than Ey and instead of the vertical coordinate Y of thecurrent pixel, the horizontal coordinate X of the current pixel p(x,y)is used. Moreover, the distance δy₁ shall be the same for a columnrather than for a row of pixels of a neighboring block (adjacent block)adjacent to the current block to be predicted. The present invention andEmbodiments may be applied to this example in a corresponding way.

FIG. 4D illustrates another example of a possible edge direction. Theedge intersects the left boundary of the block to be predicted. However,unlike the example described with reference to FIG. 4C, the edge 482cutting the left block boundary continues through the block and cuts abottom boundary of the top right neighboring block (arrow 481 in FIG.4D). In that case, the prediction is an interpolation of the edge fromtwo directions. If the present invention is applied to intra-predictionin a system with raster scan of blocks for coding/decoding, the topright neighbor of the block to be interpolated is already coded/decodedand thus, its pixels may also be utilized for the prediction. In theprevious examples, the prediction was performed by weighting two pixelsin the full-pel positions surrounding the intersection. However, theprediction may also be performed by weighting four pixels: two pixelssurrounding the intersection of the left block boundary and two pixelssurrounding the intersection of the top right boundary. The weightingfactors may further consider the distance of the particular intersectionfrom the pixel to be predicted.

For simplicity, all the above examples have been described for a blockof 4×4 pixels. However, the present invention is not limited to suchblocks. In general, any other square and rectangular sizes of blockssuch as 8×8, 16×16, 8×16, 4×8, etc. may be interpolated as describedabove.

Moreover, the above examples have been described mainly for deploymentin image or video encoders and decoders. However, the present inventionis not limited thereto. The present invention may readily be applied forother image processing tasks in which spatial extrapolation orinterpolation is required. For instance, the extrapolation/interpolationaccording to the present invention may be used for post-processing suchas error concealment.

FIG. 5 summarizes the spatial prediction of a block of pixels (block)according to the present invention employed in video coding/decoding forintra prediction. First, each of the intra prediction units 170 and 270detects an edge (Step S510), and determines whether or not the edge isdetected (Step S520). In other words, a dominant edge along which theextrapolation or interpolation is to be performed is detected. If thereis no edge detected (“no” in Step 520), meaning that the neighborhood ofthe block to be predicted is substantially smooth, each of the intraprediction units 170 and 270 applies a so-called DC interpolation(prediction using a DC prediction mode) to the block to be predicted(Step S530). The DC interpolation sets all pixels of the block to bepredicted to the same value given by the average value of the adjacentpixels. If, on the other hand, an edge is detected (“yes” in Step 520),each of the intra prediction units 170 and 270 calculates the integerslope of the edge (Step S540).

Then, each of the intra prediction units 170 and 270 determines whetheror not the current pixel to be predicted (next pixel) is present (StepS550). When determining the presence, it determines the intersection ofthe edge with the block boundaries (Step S560). Furthermore, each of theintra prediction units 170 and 270 interpolates the intersecting sub-pelposition(s) (pixel value of the sub-pixel) if necessary (Step S570), andaccordingly extrapolates or interpolates the pixel in the current pixelto be predicted, using the pixel value of the sub-pixel (Step S580).When determining no current pixel to be predicted (“no” in Step S550),each of the intra prediction units 170 and 270 ends the spatialprediction for the current block.

As illustrated in FIGS. 2 and 3, the intra prediction unit 170 in theencoder 100 and the intra prediction unit 270 in the decoder 200 performthe spatial prediction according to Embodiment 1. In particular, theintra prediction unit 170 or 270 may further include an edge detectionunit (detection unit), an intersection determining unit (determiningunit), an interpolating unit that interpolates the sub-pel positions inneighboring blocks, and an extrapolating/interpolating unit (predictionunit). The edge detection unit detects a dominant edge cutting the blockto be predicted. The intersection determining unit determines thesub-pel position corresponding to the intersection of the edgedetermined by the edge detection unit, and the row or column of pixelsbelonging to neighboring blocks surrounding the block to be predicted.The interpolating unit interpolates the pixel value of the sub-pelposition calculated by the intersection determining unit based on thevalue of the closest full pel. The extrapolating/interpolating unitextrapolates/interpolates the pixel value of the current pixel (pixelwithin the current block to be predicted) based on the sub-pelposition(s) calculated by the intersection determining unit.

In the above examples, an image is coded and/or decoded in a raster scanof blocks. The adjacent blocks available for prediction are always theblocks on the top of the block to be predicted and the blocks left fromthe block to be predicted. However, the present invention will also workfor different scans as long as there is at least one block alreadycoded/decoded adjacent to the block to be predicted or as long as thereis an edge cutting the block to be predicted and passing the adjacentblock.

The above examples have been described for a single block of pixels.Indeed, an image subdivided into a plurality of blocks may be codedusing different coding methods for each of the blocks. Error concealmentmay also be applied to single blocks. However, the present invention mayalso be applied to code an entire image or frame of a video sequence.

FIG. 6 illustrates an example system for transferring a bitstreamincluding a coded video image from an encoder to a decoder in accordancewith the present invention. The system includes an encoder 1401, achannel 1402, and a decoder 1403. The encoder 1401 corresponds to theencoder 100, and the decoder 1403 corresponds to the decoder 200.

The encoder (transmitter) 1401 codes an input video signal, andtransmits the resulting signal to the channel 1402. The encoder 1401performs coding including the directional spatial prediction inaccordance with any of Embodiments of the present invention for intraprediction of at least one block as described above. The channel 1402 iseither a storage or any transmission channel. The storage may be, forinstance, any volatile or non-volatile memory, any magnetic or opticalmedium, a mass-storage, etc. The transmission channel may be formed byphysical resources of any transmission system, wireless or wired, fixedor mobile, such as xDSL, ISDN, WLAN, GPRS, UMTS, Internet, or anystandardized or proprietary system.

The encoder 1401 may perform format conversion on the input videosignal, and include a transmitter for transferring a bitstream over thechannel 1402. Furthermore, the encoder 1401 may include an applicationfor transferring a bitstream to the storage.

The bitstream is then obtained by the decoder (receiver) 1403 throughthe channel 1402. The decoder 1403 implements the directional spatialprediction in accordance with Embodiment 1 of the present invention asdescribed above, and decodes the bitstream.

The decoder 1403 may include a receiver for receiving the bitstreamthrough the channel 1402, or an application for extracting the bitstreamfrom the storage. Furthermore, the decoder 1403 may include apost-processing unit for post processing the decoded video signal, suchas format conversion.

Summarizing, the present invention relates to an efficientimplementation of directional spatial prediction. The directionalspatial prediction includes detecting an edge by means of determining avertical gradient and a horizontal gradient within an adjacent block,determining for each pixel to be predicted an intersection of thedetected edge with a row or a column of pixels of the adjacent block,and extrapolating or interpolating each pixel (pixel to be predicted) inthe block according to the determined intersection. The intersection maybe a sub-pel position. In particular, the calculation of theintersection includes dividing by a vertical gradient or a horizontalgradient to obtain an integer slope common for the entire block to bepredicted. This reduces the number of divisions to one per block. Inorder to increase the precision of the division, a scaling by a scalingfactor depending on a value of a horizontal gradient or a verticalgradient may be applied. In other words, processes of the spatialprediction method according to the present invention are performed asindicated in FIG. 7.

FIG. 7 indicates the spatial prediction method according to an aspect ofthe present invention.

The spatial prediction method is a method for spatially predicting apixel value at each pixel position within a current block included in animage. First, the intra prediction unit 170 detects an edge E thatoverlaps the current block by obtaining the horizontal gradient Gy andthe vertical gradient Gx between pixels within the adjacent blockadjacent to the current block (Step S10). Next, the intra predictionunit 170 calculates an integer slope indicating an integer value of aslope of the detected edge, based on at least one of the obtainedhorizontal gradient Gy and the vertical gradient Gx (Step S11). Next,the intra prediction unit 170 determines, for each of the pixelpositions within the current block, the sub-pel 450 that is anintersection between (i) a line 430 that has the calculated integerslope and passes through the pixel position 440 and (ii) a boundary ofthe adjacent block (Step S12). Next, the intra prediction unit 170predicts (extrapolates or interpolates), for each of the pixelpositions, a pixel value at the pixel position 440, based on a valueinterpolated in the sub-pel position 450 determined for the pixelposition 440 (Step S13). Here, the boundary of the adjacent block is arow or a column that is the closest to the current block, among aplurality of rows or a plurality of columns of pixels included in theadjacent block. The intra prediction unit 270 also performs suchprocesses.

The integer slope has only to be calculated based on at least one of thehorizontal gradient Gy and the vertical gradient Gx, and the twogradients do not necessarily have to be used for the calculation.

Furthermore, although the image coding apparatus 100 includes the motioncompensated prediction unit 160 and others as the constituent elementsother than the intra prediction unit 170, it has only to include atleast the subtracting unit 105 and the intra prediction unit 170, anddoes not have to include the other constituent elements.

Furthermore, although the image decoding apparatus 200 includes themotion compensated prediction unit 260 and others as the constituentelements other than the intra prediction unit 270, it has only toinclude at least the adding unit 225 and the intra prediction unit 270,and does not have to include the other constituent elements.

According to Embodiment 1, the image coding apparatus 100 entropy-codesthe intra-prediction mode information, and outputs the entropy-codedintra-prediction mode information, and the image decoding apparatus 200entropy-decodes the intra-prediction mode information. Here, theintra-prediction mode information may be information indicating thedirectional intra-prediction modes, and may be information indicatingthat only intra prediction is applied to the current block to be codedor decoded, without indicating the directional intra-prediction modes.

Embodiment 2

An independent computer system can easily perform processing describedin each of Embodiments by recording, in a recording medium, a programfor implementing the structure of the video coding method (image codingmethod) or the video decoding method (image decoding method) accordingto Embodiment 1. The recording medium may be any as long as the programcan be recorded therein, such as a magnetic disk, an optical disk, anoptical magnetic disk, and a semiconductor memory.

Hereinafter, applications of the video coding method and the videodecoding method according to each of Embodiments, and a system usingsuch applications will be described.

FIG. 8 illustrates an overall configuration of a content providingsystem ex100 for implementing content distribution services. The areafor providing communication services is divided into cells of desiredsize, and base stations ex106 to ex110 which are fixed wireless stationsare placed in each of the cells.

The content providing system ex100 is connected to devices, such as acomputer ex111, a personal digital assistant (PDA) ex112, a cameraex113, a cellular phone ex114 and a game machine ex115, via an Internetex101, an Internet service provider ex102, a telephone network ex104, aswell as the base stations ex106 to ex110.

However, the configuration of the content providing system ex100 is notlimited to the configuration shown in FIG. 8, and a combination in whichany of the elements are connected is acceptable. In addition, each ofthe devices may be directly connected to the telephone network ex104,rather than via the base stations ex106 to ex110 which are the fixedwireless stations. Furthermore, the devices may be interconnected toeach other via a short distance wireless communication and others.

The camera ex113, such as a digital video camera, is capable ofcapturing moving images. A camera ex116, such as a digital video camera,is capable of capturing both still images and moving images.Furthermore, the cellular phone ex114 may be the one that meets any ofthe standards such as Global System for Mobile Communications (GSM),Code Division Multiple Access (CDMA), Wideband-Code Division MultipleAccess (W-CDMA), Long Term Evolution (LTE), and High Speed Packet Access(HSPA). Alternatively, the cellular phone ex114 may be a PersonalHandyphone System (PHS).

In the content providing system ex100, a streaming server ex103 isconnected to the camera ex113 and others via the telephone network ex104and the base station ex109, which enables distribution of a live showand others. For such a distribution, a content (for example, video of amusic live show) captured by the user using the camera ex113 is coded asdescribed above in each of Embodiments, and the coded content istransmitted to the streaming server ex103. On the other hand, thestreaming server ex103 carries out stream distribution of the receivedcontent data to the clients upon their requests. The clients include thecomputer ex111, the PDA ex112, the camera ex113, the cellular phoneex114, and the game machine ex115 that are capable of decoding theabove-mentioned coded data. Each of the devices that have received thedistributed data decodes and reproduces the coded data.

The captured data may be coded by the camera ex113 or the streamingserver ex103 that transmits the data, or the coding processes may beshared between the camera ex113 and the streaming server ex103.Similarly, the distributed data may be decoded by the clients or thestreaming server ex103, or the decoding processes may be shared betweenthe clients and the streaming server ex103. Furthermore, the data of thestill images and moving images captured by not only the camera ex113 butalso the camera ex116 may be transmitted to the streaming server ex103through the computer ex111. The coding processes may be performed by thecamera ex116, the computer ex111, or the streaming server ex103, orshared among them.

Furthermore, generally, the computer ex111 and an LSI ex500 included ineach of the devices perform such coding and decoding processes. The LSIex500 may be configured of a single chip or a plurality of chips.Software for coding and decoding moving images may be integrated intosome type of a recording medium (such as a CD-ROM, a flexible disk, ahard disk) that is readable by the computer ex111 and others, and thecoding and decoding processes may be performed using the software.Furthermore, when the cellular phone ex114 is equipped with a camera,the video data obtained by the camera may be transmitted. The video datais data coded by the LSI ex500 included in the cellular phone ex114.

Furthermore, the streaming server ex103 may be composed of servers andcomputers, and may decentralize data and process the decentralized data,record, or distribute data.

As described above, the clients can receive and reproduce the coded datain the content providing system ex100. In other words, the clients canreceive and decode information transmitted by the user, and reproducethe decoded data in real time in the content providing system ex100, sothat the user who does not have any particular right and equipment canimplement personal broadcasting.

The present invention is not limited to the above-mentioned contentproviding system ex100, and at least either the video coding apparatusor the video decoding apparatus described in each of Embodiments can beincorporated into a digital broadcasting system ex200 as shown in FIG.9. More specifically, a broadcast station ex201 communicates ortransmits, via radio waves to a broadcast satellite ex202, multiplexeddata obtained by multiplexing the audio data and the video data. Thevideo data is data coded according to the video coding method describedin each of Embodiments. Upon receipt of the video data, the broadcastsatellite ex202 transmits radio waves for broadcasting. Then, a home-useantenna ex204 capable of receiving a satellite broadcast receives theradio waves. A device, such as a television (receiver) ex300 and a settop box (STB) ex217, decodes the received multiplexed data andreproduces the data.

Furthermore, a reader/recorder ex218 that (i) reads and decodes themultiplexed data recorded on a recording media ex215, such as a DVD anda BD, or (ii) codes video signals in the recording medium ex215, and insome cases, writes data obtained by multiplexing an audio signal on thecoded data can include the video decoding apparatus or the video codingapparatus as shown in each of Embodiments. In this case, the reproducedvideo signals are displayed on the monitor ex219, and another apparatusor system can reproduce the video signals, using the recording mediumex215 on which the multiplexed data is recorded. Furthermore, it is alsopossible to implement the video decoding apparatus in the set top boxex217 connected to the cable ex203 for a cable television or the antennaex204 for satellite and/or terrestrial broadcasting, so as to displaythe video signals on the monitor ex219 of the television ex300. Thevideo decoding apparatus may be included not in the set top box but inthe television ex300.

FIG. 10 illustrates the television (receiver) ex300 that uses the videocoding method and the video decoding method described in each ofEmbodiments. The television ex300 includes: a tuner ex301 that obtainsor provides multiplexed data obtained by multiplexing the audio data andthe video data through the antenna ex204 or the cable ex203, etc. thatreceives a broadcast; a modulation/demodulation unit ex302 thatdemodulates the received multiplexed data or modulates data intomultiplexed data to be supplied outside; and amultiplexing/demultiplexing unit ex303 that demultiplexes the modulatedmultiplexed data into video data and audio data, or multiplexes thevideo data and audio data coded by the signal processing unit ex306 intodata. Furthermore, the television ex300 further includes: a signalprocessing unit ex306 including an audio signal processing unit ex304and a video signal processing unit ex305 that decode audio data andvideo data and code audio data and video data, respectively; a speakerex307 that provides the decoded audio signal; and an output unit ex309including a display unit ex308 that displays the decoded video signal,such as a display. Furthermore, the television ex300 includes aninterface unit ex317 including an operation input unit ex312 thatreceives an input of a user operation. Furthermore, the television ex300includes a control unit ex310 that controls overall each constituentelement of the television ex300, and a power supply circuit unit ex311that supplies power to each of the elements. Other than the operationinput unit ex312, the interface unit ex317 may include: a bridge ex313that is connected to an external device, such as the reader/recorderex218; a slot unit ex314 for enabling attachment of the recording mediumex216, such as an SD card; a driver ex315 to be connected to an externalrecording medium, such as a hard disk; and a modem ex316 to be connectedto a telephone network. Here, the recording medium ex216 canelectrically record information using a non-volatile/volatilesemiconductor memory element for storage. The constituent elements ofthe television ex300 are connected to one another through a synchronousbus.

First, a configuration in which the television ex300 decodes themultiplexed data obtained from outside through the antenna ex204 andothers and reproduces the decoded data will be described. In thetelevision ex300, upon receipt of a user operation from a remotecontroller ex220 and others, the multiplexing/demultiplexing unit ex303demultiplexes the multiplexed data demodulated by themodulation/demodulation unit ex302, under control of the control unitex310 including a CPU. Furthermore, the audio signal processing unitex304 decodes the demultiplexed audio data, and the video signalprocessing unit ex305 decodes the demultiplexed video data, using thedecoding method described in each of Embodiments, in the televisionex300. The output unit ex309 provides the decoded video signal and audiosignal outside. When the output unit ex309 provides the video signal andthe audio signal, the signals may be temporarily stored in buffers ex318and ex319, and others so that the signals are reproduced insynchronization with each other. Furthermore, the television ex300 mayread the multiplexed data not through a broadcast and others but fromthe recording media ex215 and ex216, such as a magnetic disk, an opticaldisc, and an SD card. Next, a configuration in which the televisionex300 codes an audio signal and a video signal, and transmits the dataoutside or writes the data on a recording medium will be described. Inthe television ex300, upon receipt of a user operation from the remotecontroller ex220 and others, the audio signal processing unit ex304codes an audio signal, and the video signal processing unit ex305 codesa video signal, under control of the control unit ex310 using the codingmethod as described in each of Embodiments. Themultiplexing/demultiplexing unit ex303 multiplexes the coded videosignal and audio signal, and provides the resulting signal outside. Whenthe multiplexing/demultiplexing unit ex303 multiplexes the video signaland the audio signal, the signals may be temporarily stored in buffersex320 and ex321, and others so that the signals are reproduced insynchronization with each other. Here, the buffers ex318 to ex321 may beplural as illustrated, or at least one buffer may be shared in thetelevision ex300. Furthermore, data may be stored in a buffer other thanthe buffers ex318 to ex321 so that the system overflow and underflow maybe avoided between the modulation/demodulation unit ex302 and themultiplexing/demultiplexing unit ex303, for example.

Furthermore, the television ex300 may include a configuration forreceiving an AV input from a microphone or a camera other than theconfiguration for obtaining audio and video data from a broadcast or arecording medium, and may code the obtained data. Although thetelevision ex300 can code, multiplex, and provide outside data in thedescription, it may be not capable of performing all the processes butcapable of only one of receiving, decoding, and providing outside data.

Furthermore, when the reader/recorder ex218 reads or writes themultiplexed data from or in a recording medium, one of the televisionex300 and the reader/recorder ex218 may decode or code the multiplexeddata, and the television ex300 and the reader/recorder ex218 may sharethe decoding or coding.

As an example, FIG. 11 illustrates a configuration of an informationreproducing/recording unit ex400 when data is read or written from or inan optical disc. The information reproducing/recording unit ex400includes constituent elements ex401 to ex407 to be describedhereinafter. The optical head ex401 irradiates a laser spot on arecording surface of the recording medium ex215 that is an optical discto write information, and detects reflected light from the recordingsurface of the recording medium ex215 to read the information. Themodulation recording unit ex402 electrically drives a semiconductorlaser included in the optical head ex401, and modulates the laser lightaccording to recorded data. The reproduction demodulating unit ex403amplifies a reproduction signal obtained by electrically detecting thereflected light from the recording surface using a photo detectorincluded in the optical head ex401, and demodulates the reproductionsignal by separating a signal component recorded on the recording mediumex215 to reproduce the necessary information. The buffer ex404temporarily holds the information to be recorded on the recording mediumex215 and the information reproduced from the recording medium ex215. Adisk motor ex405 rotates the recording medium ex215. A servo controlunit ex406 moves the optical head ex401 to a predetermined informationtrack while controlling the rotation drive of the disk motor ex405 so asto follow the laser spot. The system control unit ex407 controls overallthe information reproducing/recording unit ex400. The reading andwriting processes can be implemented by the system control unit ex407using various information stored in the buffer ex404 and generating andadding new information as necessary, and by the modulation recordingunit ex402, the reproduction demodulating unit ex403, and the servocontrol unit ex406 that record and reproduce information through theoptical head ex401 while being operated in a coordinated manner. Thesystem control unit ex407 includes, for example, a microprocessor, andexecutes processing by causing a computer to execute a program for readand write.

Although the optical head ex401 irradiates a laser spot in thedescription, it may perform high-density recording using near fieldlight.

FIG. 12 schematically illustrates the recording medium ex215 that is theoptical disc. On the recording surface of the recording medium ex215,guide grooves are spirally formed, and an information track ex230records, in advance, address information indicating an absolute positionon the disk according to change in a shape of the guide grooves. Theaddress information includes information for determining positions ofrecording blocks ex231 that are a unit for recording data. An apparatusthat records and reproduces data reproduces the information track ex230and reads the address information so as to determine the positions ofthe recording blocks. Furthermore, the recording medium ex215 includes adata recording area ex233, an inner circumference area ex232, and anouter circumference area ex234. The data recording area ex233 is an areafor use in recording the user data. The inner circumference area ex232and the outer circumference area ex234 that are inside and outside ofthe data recording area ex233, respectively are for specific use exceptfor recording the user data. The information reproducing/recording unit400 reads and writes coded audio data, coded video data, or multiplexeddata obtained by multiplexing the coded audio data and the coded videodata, from and on the data recording area ex233 of the recording mediumex215.

Although an optical disc having a layer, such as a DVD and a BD isdescribed as an example in the description, the optical disc is notlimited to such, and may be an optical disc having a multilayerstructure and capable of being recorded on a part other than thesurface. Furthermore, the optical disc may have a structure formultidimensional recording/reproduction, such as recording ofinformation using light of colors with different wavelengths in the sameportion of the optical disc and recording information having differentlayers from various angles.

Furthermore, the car ex210 having the antenna ex205 can receive datafrom the satellite ex202 and others, and reproduce video on the displaydevice such as the car navigation system ex211 set in the car ex210, ina digital broadcasting system ex200. Here, a configuration of the carnavigation system ex211 will be the one for example, including a GPSreceiving unit in the configuration illustrated in FIG. 10. The samewill be true for the configuration of the computer ex111, the cellularphone ex114, and others.

FIG. 13A illustrates the cellular phone ex114 that uses the video codingmethod and the video decoding method described in each of Embodiments.The cellular phone ex114 includes: an antenna ex350 for transmitting andreceiving radio waves through the base station ex110; a camera unitex365 capable of capturing moving and still images; and a display unitex358 such as a liquid crystal display for displaying the data such asdecoded video captured by the camera unit ex365 or received by theantenna ex350. The cellular phone ex114 further includes: a main bodyunit including a set of operation keys ex366; an audio output unit ex357such as a speaker for output of audio; an audio input unit ex356 such asa microphone for input of audio; a memory unit ex367 for storingcaptured video or still pictures, recorded audio, coded or decoded dataof the received video, the still images, e-mails, or others; and a slotunit ex364 that is an interface unit for a recording medium that storesdata in the same manner as the memory unit ex367.

Next, an example of a configuration of the cellular phone ex114 will bedescribed with reference to FIG. 13B. In the cellular phone ex114, amain control unit ex360 designed to control overall each unit of themain body including the display unit ex358 as well as the operation keysex366 is connected mutually, via a synchronous bus ex370, to a powersupply circuit unit ex361, an operation input control unit ex362, avideo signal processing unit ex355, a camera interface unit ex363, aliquid crystal display (LCD) control unit ex359, amodulation/demodulation unit ex352, a multiplexing/demultiplexing unitex353, an audio signal processing unit ex354, the slot unit ex364, andthe memory unit ex367.

When a call-end key or a power key is turned ON by a user's operation,the power supply circuit unit ex361 supplies the respective units withpower from a battery pack so as to activate the cell phone ex114.

In the cellular phone ex114, the audio signal processing unit ex354converts the audio signals collected by the audio input unit ex356 invoice conversation mode into digital audio signals under the control ofthe main control unit ex360 including a CPU, ROM, and RAM. Also, in thecellular phone ex114, the transmitting and receiving unit ex351amplifies the data received by the antenna ex350 in voice conversationmode and performs frequency conversion and the analog-to-digitalconversion on the data. Then, the modulation/demodulation unit ex352performs inverse spread spectrum processing on the data, and the audiosignal processing unit ex354 converts it into analog audio signals, soas to output them via the audio output unit ex356.

Furthermore, when an e-mail in data communication mode is transmitted,text data of the e-mail inputted by operating the operation keys ex366and others of the main body is sent out to the main control unit ex360via the operation input control unit ex362. The main control unit ex360causes the modulation/demodulation unit ex352 to perform spread spectrumprocessing on the text data, and the transmitting and receiving unitex351 performs the digital-to-analog conversion and the frequencyconversion on the resulting data to transmit the data to the basestation ex110 via the antenna ex350. When an e-mail is received,processing that is approximately inverse to the processing fortransmitting an e-mail is performed on the received data, and theresulting data is provided to the display unit ex358.

When video, still images, or video and audio in data communication modeis or are transmitted, the video signal processing unit ex355 compressesand codes video signals supplied from the camera unit ex365 using themoving image coding method shown in each of Embodiments, and transmitsthe coded video data to the multiplexing/demultiplexing unit ex353. Incontrast, during the time when the camera unit ex365 captures video,still images, and others, the audio signal processing unit ex354 codesaudio signals collected by the audio input unit ex356, and transmits thecoded audio data to the multiplexing/demultiplexing unit ex353.

The multiplexing/demultiplexing unit ex353 multiplexes the coded videodata supplied from the video signal processing unit ex355 and the codedaudio data supplied from the audio signal processing unit ex354, using apredetermined method. Then, the modulation/demodulation unit ex352performs spread spectrum processing on the multiplexed data, and thetransmitting and receiving unit ex351 performs digital-to-analogconversion and frequency conversion on the data so as to transmit theresulting data via the antenna ex350.

When receiving data of a video file which is linked to a Web page andothers in data communication mode or when receiving an e-mail with videoand/or audio attached, in order to decode the multiplexed data receivedvia the antenna ex350, the multiplexing/demultiplexing unit ex353demultiplexes the multiplexed data into a video data bit stream and anaudio data bit stream, and supplies the video signal processing unitex355 with the coded video data and the audio signal processing unitex354 with the coded audio data, through the synchronous bus ex370. Thevideo signal processing unit ex355 decodes the video signal using avideo decoding method corresponding to the video coding method shown ineach of Embodiments, and then the display unit ex358 displays, forinstance, the video and still images included in the video file linkedto the Web page via the LCD control unit ex359. Furthermore, the audiosignal processing unit ex354 decodes the audio signal, and the audiooutput unit ex357 provides the audio.

Furthermore, similarly to the television ex300, a terminal such as thecellular phone ex114 probably have 3 types of implementationconfigurations including not only (i) a transmitting and receivingterminal including both a coding apparatus and a decoding apparatus, butalso (ii) a transmitting terminal including only a coding apparatus and(iii) a receiving terminal including only a decoding. apparatus.Although the digital broadcasting system ex200 receives and transmitsthe multiplexed data obtained by multiplexing audio data onto video datain the description, the multiplexed data may be data obtained bymultiplexing not audio data but character data related to video ontovideo data, and may be not multiplexed data but video data itself.

As such, the video coding method and the video decoding method in eachof Embodiments can be used in any of the devices and systems described.Thus, the advantages described in each of Embodiments can be obtained.

Furthermore, the present invention is not limited to Embodiments, andvarious modifications and revisions are possible without departing fromthe scope of the present invention.

Embodiment 3

Video data can be generated by switching, as necessary, between (i) themoving image coding method or the moving image coding apparatus shown ineach of Embodiments and (ii) a moving image coding method or a movingimage coding apparatus in conformity with a different standard, such asMPEG-2, MPEG4-AVC, and VC-1.

Here, when a plurality of video data that conforms to the differentstandards is generated and is then decoded, the decoding methods need tobe selected to conform to the different standards. However, since towhich standard each of the plurality of the video data to be decodedconforms cannot be detected, there is a problem that an appropriatedecoding method cannot be selected.

In order to solve the problem, multiplexed data obtained by multiplexingaudio data and others onto video data has a structure includingidentification information indicating to which standard the video dataconforms. The specific structure of the multiplexed data including thevideo data generated in the moving image coding method and by the movingimage coding apparatus shown in each of Embodiments will be hereinafterdescribed. The multiplexed data is a digital stream in the MPEG-2Transport Stream format.

FIG. 14 illustrates a structure of multiplexed data. As illustrated inFIG. 14, the multiplexed data can be obtained by multiplexing at leastone of a video stream, an audio stream, a presentation graphics stream(PG), and an interactive graphics stream. The video stream representsprimary video and secondary video of a movie, the audio stream (IG)represents a primary audio part and a secondary audio part to be mixedwith the primary audio part, and the presentation graphics streamrepresents subtitles of a movie. Here, the primary video is normal videoto be displayed on a screen, and the secondary video is video to bedisplayed on a smaller window in the main video. Furthermore, theinteractive graphics stream represents an interactive screen to begenerated by arranging the GUI components on a screen. The video streamis coded in the video coding method or by the video coding apparatusshown in each of Embodiments, or in a video coding method or by a videocoding apparatus in conformity with a conventional standard, such asMPEG-2, MPEG4-AVC, and VC-1. The audio stream is coded in accordancewith a standard, such as Dolby-AC-3, Dolby Digital Plus, MLP, DTS,DTS-HD, and linear PCM.

Each stream included in the multiplexed data is identified by PID. Forexample, 0x1011 is allocated to the video stream to be used for video ofa movie, 0x1100 to 0x111F are allocated to the audio streams, 0x1200 to0x121F are allocated to the presentation graphics streams, 0x1400 to0x141F are allocated to the interactive graphics streams, 0x1B00 to0x1B1F are allocated to the video streams to be used for secondary videoof the movie, and 0x1A00 to 0x1A1F are allocated to the audio streams tobe used for the secondary video to be mixed with the primary audio.

FIG. 15 schematically illustrates how data is multiplexed. First, avideo stream ex235 composed of video frames and an audio stream ex238composed of audio frames are transformed into a stream of PES packetsex236 and a stream of PES packets ex239, and further into TS packetsex237 and TS packets ex240, respectively. Similarly, data of apresentation graphics stream ex241 and data of an interactive graphicsstream ex244 are transformed into a stream of PES packets ex242 and astream of PES packets ex245, and further into TS packets ex243 and TSpackets ex246, respectively. These TS packets are multiplexed into astream to obtain multiplexed data ex247.

FIG. 16 illustrates how a video stream is stored in a stream of PESpackets in more detail. The first bar in FIG. 16 shows a video framestream in a video stream. The second bar shows the stream of PESpackets. As indicated by arrows denoted as yy1, yy2, yy3, and yy4 inFIG. 16, the video stream is divided into pictures as I pictures, Bpictures, and P pictures each of which is a video presentation unit, andthe pictures are stored in a payload of each of the PES packets. Each ofthe PES packets has a PES header, and the PES header stores aPresentation Time-Stamp (PTS) indicating a display time of the picture,and a Decoding Time-Stamp (DTS) indicating a decoding time of thepicture.

FIG. 17 illustrates a format of TS packets to be finally written on themultiplexed data. Each of the TS packets is a 188-byte fixed lengthpacket including a 4-byte TS header having information, such as a PIDfor identifying a stream and a 184-byte TS payload for storing data. ThePES packets are divided, and stored in the TS payloads, respectively.When a BD ROM is used, each of the TS packets is given a 4-byteTP_Extra_Header, thus resulting in 192-byte source packets. The sourcepackets are written on the multiplexed data. The TP_Extra_Header storesinformation such as an Arrival_Time_Stamp (ATS). The ATS shows atransfer start time at which each of the TS packets is to be transferredto a PID filter. The numbers incrementing from the head of themultiplexed data are called source packet numbers (SPNs) as shown at thebottom of FIG. 17.

Each of the TS packets included in the multiplexed data includes notonly streams of audio, video, subtitles and others, but also a ProgramAssociation Table (PAT), a Program Map Table (PMT), and a Program ClockReference (PCR). The PAT shows what a PID in a PMT used in themultiplexed data indicates, and a PID of the PAT itself is registered aszero. The PMT stores PIDs of the streams of video, audio, subtitles andothers included in the multiplexed data, and attribute information ofthe streams corresponding to the PIDs. The PMT also has variousdescriptors relating to the multiplexed data. The descriptors haveinformation such as copy control information showing whether copying ofthe multiplexed data is permitted or not. The PCR stores STC timeinformation corresponding to an ATS showing when the PCR packet istransferred to a decoder, in order to achieve synchronization between anArrival Time Clock (ATC) that is a time axis of ATSs, and an System TimeClock (STC) that is a time axis of PTSs and DTSs.

FIG. 18 illustrates the data structure of the PMT in detail. A PMTheader is disposed at the top of the PMT. The PMT header describes thelength of data included in the PMT and others. A plurality ofdescriptors relating to the multiplexed data is disposed after the PMTheader. Information such as the copy control information is described inthe descriptors. After the descriptors, a plurality of pieces of streaminformation relating to the streams included in the multiplexed data isdisposed. Each piece of stream information includes stream descriptorseach describing information, such as a stream type for identifying acompression codec of a stream, a stream PID, and stream attributeinformation (such as a frame rate or an aspect ratio). The streamdescriptors are equal in number to the number of streams in themultiplexed data.

When the multiplexed data is recorded on a recording medium and others,it is recorded together with multiplexed data information files.

Each of the multiplexed data information files is management informationof the multiplexed data as shown in FIG. 19. The multiplexed datainformation files are in one to one correspondence with the multiplexeddata, and each of the files includes multiplexed data information,stream attribute information, and an entry map.

As illustrated in FIG. 19, the multiplexed data information includes asystem rate, a reproduction start time, and a reproduction end time. Thesystem rate indicates the maximum transfer rate at which a system targetdecoder to be described later transfers the multiplexed data to a PIDfilter. The intervals of the ATSs included in the multiplexed data areset to not higher than a system rate. The reproduction start timeindicates a PTS in a video frame at the head of the multiplexed data. Aninterval of one frame is added to a PTS in a video frame at the end ofthe multiplexed data, and the PTS is set to the reproduction end time.

As shown in FIG. 20, a piece of attribute information is registered inthe stream attribute information, for each PID of each stream includedin the multiplexed data. Each piece of attribute information hasdifferent information depending on whether the corresponding stream is avideo stream, an audio stream, a presentation graphics stream, or aninteractive graphics stream. Each piece of video stream attributeinformation carries information including what kind of compression codecis used for compressing the video stream, and the resolution, aspectratio and frame rate of the pieces of picture data that is included inthe video stream. Each piece of audio stream attribute informationcarries information including what kind of compression codec is used forcompressing the audio stream, how many channels are included in theaudio stream, which language the audio stream supports, and how high thesampling frequency is. The video stream attribute information and theaudio stream attribute information are used for initialization of adecoder before the player plays back the information.

In Embodiment 3, the multiplexed data to be used is of a stream typeincluded in the PMT. Furthermore, when the multiplexed data is recordedon a recording medium, the video stream attribute information includedin the multiplexed data information is used. More specifically, thevideo coding method or the video coding apparatus described in each ofEmbodiments includes a step or a unit for allocating unique informationindicating video data generated by the video coding method or the videocoding apparatus in each of Embodiments, to the stream type included inthe PMT or the video stream attribute information. With the structure,the video data generated by the video coding method or the video codingapparatus described in each of Embodiments can be distinguished fromvideo data that conforms to another standard.

Furthermore, FIG. 21 illustrates steps of the video decoding methodaccording to Embodiment 3. In Step exS100, the stream type included inthe PMT or the video stream attribute information is obtained from themultiplexed data. Next, in Step exS101, it is determined whether or notthe stream type or the video stream attribute information indicates thatthe multiplexed data is generated by the video coding method or thevideo coding apparatus in each of Embodiments. When it is determinedthat the stream type or the video stream attribute information indicatesthat the multiplexed data is generated by the video coding method or thevideo coding apparatus in each of Embodiments, in Step exS102, thestream type or the video stream attribute information is decoded by thevideo decoding method in each of Embodiments. Furthermore, when thestream type or the video stream attribute information indicatesconformance to the conventional standards, such as MPEG-2, MPEG4-AVC,and VC-1, in Step exS103, the stream type or the video stream attributeinformation is decoded by a video decoding method in conformity with theconventional standards.

As such, allocating a new unique value to the stream type or the videostream attribute information enables determination whether or not thevideo decoding method or the video decoding apparatus that is describedin each of Embodiments can perform decoding. Even upon an input ofmultiplexed data that conforms to a different standard, an appropriatedecoding method or apparatus can be selected. Thus, it becomes possibleto decode information without any error. Furthermore, the video codingmethod or apparatus, or the video decoding method or apparatus inEmbodiment 3 can be used in the devices and systems described above.

Embodiment 4

Each of the video coding method, the video coding apparatus, the videodecoding method, and the video decoding apparatus in each of Embodimentsis typically achieved in the form of an integrated circuit or a LargeScale Integrated (LSI) circuit. As an example of the LSI, FIG. 22illustrates a configuration of the LSI ex500 that is made into one chip.The LSI ex500 includes elements ex501, ex502, ex503, ex504, ex505,ex506, ex507, ex508, and ex509 to be described below, and the elementsare connected to each other through a bus ex510. The power supplycircuit unit ex505 is activated by supplying each of the elements withpower when the power supply circuit unit ex505 is turned on.

For example, when coding is performed, the LSI ex500 receives an AVsignal from a microphone ex117, a camera ex113, and others through an AVIO ex509 under control of a control unit ex501 including a CPU ex502, amemory controller ex503, a stream controller ex504, and a drivingfrequency control unit ex512. The received AV signal is temporarilystored in an external memory ex511, such as an SDRAM. Under control ofthe control unit ex501, the stored data is segmented into data portionsaccording to the processing amount and speed to be transmitted to asignal processing unit ex507. Then, the signal processing unit ex507codes an audio signal and/or a video signal. Here, the coding of thevideo signal is the coding described in each of Embodiments.Furthermore, the signal processing unit ex507 sometimes multiplexes thecoded audio data and the coded video data, and a stream IO ex506provides the multiplexed data outside. The provided multiplexed data istransmitted to the base station ex107, or written on the recording mediaex215. When data sets are multiplexed, the data sets should betemporarily stored in the buffer ex508 so that the data sets aresynchronized with each other.

Although the memory ex511 is an element outside the LSI ex500, it may beincluded in the LSI ex500. The buffer ex508 is not limited to onebuffer, but may be composed of buffers. Furthermore, the LSI ex500 maybe made into one chip or a plurality of chips.

Furthermore, although the control unit ex510 includes the CPU ex502, thememory controller ex503, the stream controller ex504, the drivingfrequency control unit ex512, the configuration of the control unitex510 is not limited to such. For example, the signal processing unitex507 may further include a CPU. Inclusion of another CPU in the signalprocessing unit ex507 can improve the processing speed. Furthermore, asanother example, the CPU ex502 may include the signal processing unitex507, or an audio signal processing unit that is a part of the signalprocessing unit ex507. In such a case, the control unit ex501 includesthe signal processing unit ex507 or the CPU ex502 including a part ofthe signal processing unit ex507.

The name used here is LSI, but it may also be called IC, system LSI,super LSI, or ultra LSI depending on the degree of integration.

Moreover, ways to achieve integration are not limited to the LSI, and aspecial circuit or a general purpose processor and so forth can alsoachieve the integration. Field Programmable Gate Array (FPGA) that canbe programmed after manufacturing LSIs or a reconfigurable processorthat allows re-configuration of the connection or configuration of anLSI can be used for the same purpose.

In the future, with advancement in semiconductor technology, a brand-newtechnology may replace LSI. The functional blocks can be integratedusing such a technology. The possibility is that the present inventionis applied to biotechnology.

Embodiment 5

When video data is decoded by the video coding method or by the videocoding apparatus described in each of Embodiments, compared to whenvideo data that conforms to a conventional standard, such as MPEG-2,MPEG4-AVC, and VC-1, the computing amount probably increases. Thus, theLSI ex500 needs to be set to a driving frequency higher than that of theCPU ex502 to be used when video data in conformity with the conventionalstandard is decoded. However, when the driving frequency is set higher,there is a problem that the power consumption increases.

In order to solve the problem, the video decoding apparatus, such as thetelevision ex300 and the LSI ex500 is configured to determine to whichstandard the video data conforms, and switch between the drivingfrequencies according to the determined standard. FIG. 23 illustrates aconfiguration ex800 in Embodiment 5. A driving frequency switching unitex803 sets a driving frequency to a higher driving frequency when videodata is generated by the video coding method or the video codingapparatus described in each of Embodiments. Then, the driving frequencyswitching unit ex803 instructs a decoding processing unit ex801 thatexecutes the video decoding method described in each of Embodiments todecode the video data. When the video data conforms to the conventionalstandard, the driving frequency switching unit ex803 sets a drivingfrequency to a lower driving frequency than that of the video datagenerated by the video coding method or the video coding apparatusdescribed in each of Embodiments. Then, the driving frequency switchingunit ex803 instructs the decoding processing unit ex802 that conforms tothe conventional standard to decode the video data.

More specifically, the driving frequency switching unit ex803 includesthe CPU ex502 and the driving frequency control unit ex512 in FIG. 22.Here, each of the decoding processing unit ex801 that executes the videodecoding method described in each of Embodiments and the decodingprocessing unit ex802 that conforms to the conventional standardcorresponds to the signal processing unit ex507 in FIG. 22. The CPUex502 determines to which standard the video data conforms. Then, thedriving frequency control unit ex512 determines a driving frequencybased on a signal from the CPU ex502. Furthermore, the signal processingunit ex507 decodes the video data based on a signal from the CPU ex502.For example, the identification information described in Embodiment 3 isprobably used for identifying the video data. The identificationinformation is not limited to the one described in Embodiment 3 but maybe any information as long as the information indicates to whichstandard the video data conforms. For example, when which standard videodata conforms to can be determined based on an external signal fordetermining that the video data is used for a television or a disk,etc., the determination may be made based on such an external signal.Furthermore, the CPU ex502 selects a driving frequency based on, forexample, a look-up table in which the standards of the video data areassociated with the driving frequencies as shown in FIG. 25. The drivingfrequency can be selected by storing the look-up table in the bufferex508 and an internal memory of an LSI and with reference to the look-uptable by the CPU ex502.

FIG. 24 illustrates steps for executing a method in Embodiment 5. First,in Step exS200, the signal processing unit ex507 obtains identificationinformation from the multiplexed data. Next, in Step exS201, the CPUex502 determines whether or not the video data is generated based on theidentification information by the coding method and the coding apparatusdescribed in each of Embodiments. When the video data is generated bythe coding method and the coding apparatus described in each ofEmbodiments, in Step exS202, the CPU ex502 transmits a signal forsetting the driving frequency to a higher driving frequency to thedriving frequency control unit ex512. Then, the driving frequencycontrol unit ex512 sets the driving frequency to the higher drivingfrequency. On the other hand, when the identification informationindicates that the video data conforms to the conventional standard,such as MPEG-2, MPEG4-AVC, and VC-1, in Step exS203, the CPU ex502transmits a signal for setting the driving frequency to a lower drivingfrequency to the driving frequency control unit ex512. Then, the drivingfrequency control unit ex512 sets the driving frequency to the lowerdriving frequency than that in the case where the video data isgenerated by the coding method and the coding apparatus described ineach of Embodiments.

Furthermore, along with the switching of the driving frequencies, thepower conservation effect can be improved by changing the voltage to beapplied to the LSI ex500 or an apparatus including the LSI ex500. Forexample, when the driving frequency is set lower, the voltage to beapplied to the LSI ex500 or the apparatus including the LSI ex500 isprobably set to a voltage lower than that in the case where the drivingfrequency is set higher.

Furthermore, when the computing amount for decoding is larger, thedriving frequency may be set higher, and when the computing amount fordecoding is smaller, the driving frequency may be set lower as themethod for setting the driving frequency. Thus, the setting method isnot limited to the ones described above. For example, when the computingamount for decoding video data in conformity with MPEG4-AVC is largerthan the computing amount for decoding video data generated by the videocoding method and the video coding apparatus described in each ofEmbodiments, the driving frequency is probably set in reverse order tothe setting described above.

Furthermore, the method for setting the driving frequency is not limitedto the method for setting the driving frequency lower. For example, whenthe identification information indicates that the video data isgenerated by the video coding method and the video coding apparatusdescribed in each of Embodiments, the voltage to be applied to the LSIex500 or the apparatus including the LSI ex500 is probably set higher.When the identification information indicates that the video dataconforms to the conventional standard, such as MPEG-2, MPEG4-AVC, andVC-1, the voltage to be applied to the LSI ex500 or the apparatusincluding the LSI ex500 is probably set lower. As another example, whenthe identification information indicates that the video data isgenerated by the video coding method and the video coding apparatusdescribed in each of Embodiments, the driving of the CPU ex502 does notprobably have to be suspended. When the identification informationindicates that the video data conforms to the conventional standard,such as MPEG-2, MPEG4-AVC, and VC-1, the driving of the CPU ex502 isprobably suspended at a given time because the CPU ex502 has extraprocessing capacity. Even when the identification information indicatesthat the video data is generated by the video coding method and thevideo coding apparatus described in each of Embodiments, in the casewhere the CPU ex502 has extra processing capacity, the driving of theCPU ex502 is probably suspended at a given time. In such a case, thesuspending time is probably set shorter than that in the case where whenthe identification information indicates that the video data conforms tothe conventional standard, such as MPEG-2, MPEG4-AVC, and VC-1.

Accordingly, the power conservation effect can be improved by switchingbetween the driving frequencies in accordance with the standard to whichthe video data conforms. Furthermore, when the LSI ex500 or theapparatus including the LSI ex500 is driven using a battery, the batterylife can be extended with the power conservation effect.

Embodiment 6

There are cases where a plurality of video data that conforms todifferent standards, is provided to the devices and systems, such as atelevision and a cellular phone. In order to enable decoding theplurality of video data that conforms to the different standards, thesignal processing unit ex507 of the LSI ex500 needs to conform to thedifferent standards. However, the problems of increase in the scale ofthe circuit of the LSI ex500 and increase in the cost arise with theindividual use of the signal processing units ex507 that conform to therespective standards.

In order to solve the problem, what is conceived is a configuration inwhich the decoding processing unit for implementing the video decodingmethod described in each of Embodiments and the decoding processing unitthat conforms to the conventional standard, such as MPEG-2, MPEG4-AVC,and VC-1 are partly shared. Ex900 in FIG. 26A shows an example of theconfiguration. For example, the video decoding method described in eachof Embodiments and the video decoding method that conforms to MPEG4-AVChave, partly in common, the details of processing, such as entropycoding, inverse quantization, deblocking filtering, and motioncompensated prediction. The details of processing to be shared probablyinclude use of a decoding processing unit ex902 that conforms toMPEG4-AVC. In contrast, a dedicated decoding processing unit ex901 isprobably used for other processing unique to the present invention. Thedecoding processing unit for implementing the video decoding methoddescribed in each of Embodiments may be shared for the processing to beshared, and a dedicated decoding processing unit may be used forprocessing unique to that of MPEG4-AVC.

Furthermore, ex1000 in FIG. 26B shows another example in whichprocessing is partly shared. This example uses a configuration includinga dedicated decoding processing unit ex1001 that supports the processingunique to the present invention, a dedicated decoding processing unitex1002 that supports the processing unique to another conventionalstandard, and a decoding processing unit ex1003 that supports processingto be shared between the video decoding method in the present inventionand the conventional video decoding method. Here, the dedicated decodingprocessing units ex1001 and ex1002 are not necessarily specialized forthe processing of the present invention and the processing of theconventional standard, and may be the ones capable of implementinggeneral processing. Furthermore, the configuration of Embodiment 6 canbe implemented by the LSI ex500.

As such, reducing the scale of the circuit of an LSI and reducing thecost are possible by sharing the decoding processing unit for theprocessing to be shared between the video decoding method in the presentinvention and the video decoding method in conformity with theconventional standard.

INDUSTRIAL APPLICABILITY

The spatial prediction method according to the present invention canreduce the complexity of the spatial prediction, and is applicable tocellular phones, personal computers, recording reproducing apparatuses,or others each of which includes, for example, at least one of (i) animage coding apparatus that codes an image using a result of the spatialprediction, (ii) an image decoding apparatus that decodes an image usinga result of the spatial prediction, and (iii) the image coding apparatusand the image decoding apparatus.

REFERENCE SIGNS LIST

-   100 Image coding apparatus (encoder)-   105 Subtracting unit-   110 Transform quantization unit-   120 Inverse quantization and inverse transform unit-   125 Adding unit-   130 Deblocking filter-   140 Memory-   150 Interpolation filter-   160 Motion compensated prediction unit-   165 Motion estimation unit-   170 Intra prediction unit-   175 Intra/inter switch unit-   180 Post filter design unit-   190 Entropy coding unit-   200 Image decoding apparatus (decoder)-   220 Inverse quantization and inverse transform unit-   225 Adding unit-   230 Deblocking filter-   240 Memory-   250 Interpolation filter-   260 Motion compensated prediction unit-   270 Intra prediction unit-   275 Intra/inter switch unit-   280 Post filter-   290 Entropy decoding unit

1. A spatial prediction method for spatially predicting a pixel value ateach pixel position within a current block included in an image, themethod comprising: calculating an integer slope based on at least one ofa horizontal gradient and a vertical gradient each of which is indicatedby a mode number, the integer slope indicating an integer value of aslope; determining a sub-pel position that is an intersection between(i) a line of the integer slope that passes through the pixel positionwithin the current block and (ii) a boundary of a block adjacent to thecurrent block; and predicting, for each of the pixel positions, thepixel value at the pixel position based on a pixel value interpolated inthe sub-pel position determined for the pixel position.
 2. The spatialprediction method according to claim 1, wherein in the calculating, theone of the horizontal gradient and the vertical gradient is scaled by ac-th power of 2, and the integer slope is calculated using the scaledone of the horizontal gradient and the vertical gradient, c being apositive integer, and in the determining, the sub-pel position for thepixel position is calculated by multiplying the integer slope generatedby the scaling by a coordinate value horizontal or vertical to the pixelposition to be predicted within the current block.
 3. The spatialprediction method according to claim 2, further comprising calculatingthe value of c using a function of the one of the horizontal gradientand the vertical gradient.
 4. The spatial prediction method according toclaim 1, wherein in the calculating, a result of a division is obtainedwith reference to a division table stored in a memory, and the integerslope is calculated using the obtained result of the division, thedivision using, as a divisor, a value indicating the one of thehorizontal gradient and the vertical gradient, and the division tableindicating, for each predetermined value, the predetermined value and aresult of a division using the predetermined value as a divisor.
 5. Thespatial prediction method according to claim 4, wherein a maximum valueof the predetermined value indicated in the division table is a b-thpower of 2, b being an integer, and in the calculating, when the valueindicating the one of the horizontal gradient and the vertical gradientused as the divisor exceeds the b-th power of 2, the one of thehorizontal gradient and the vertical gradient is scaled by shifting bitsof the value to the right to obtain the result of the division using, asa divisor, a value indicating the scaled one of the horizontal gradientand the vertical gradient.
 6. The spatial prediction method according toclaim 1, wherein in the calculating, the integer slope is calculated bydividing a value indicating one of the horizontal gradient and thevertical gradient by a value indicating the other of the horizontalgradient and the vertical gradient, when the pixel value at each of thepixel positions within the current block is predicted, weights are setaccording to a distance, in the boundary, between the sub-pel positiondetermined for the pixel position and each of full-pel positionsadjacent to the sub-pel position, and the pixel value at the sub-pelposition is interpolated by setting a corresponding one of the weightsto each pixel value of the full-pel positions and calculating a weightedaverage of the pixel values.
 7. The spatial prediction method accordingto claim 1, wherein in the calculating, the integer slope is calculatedsolely for the current block, and in the determining, the sub-pelposition is determined for each of the pixel positions within thecurrent block, using the integer slope that is common to the pixelpositions.
 8. A method for decoding an image coded per block, the methodcomprising: predicting a pixel value at each pixel position within acurrent block to be decoded, using the spatial prediction methodaccording to claim 1 to generate a predicted block; obtaining aprediction error block; and adding the predicted block to the predictionerror block.
 9. A method for coding an image per block, the methodcomprising: predicting a pixel value at each pixel position within acurrent block to be coded, using the spatial prediction method accordingto claim 1 to generate a predicted block; and subtracting the predictedblock from the current block.
 10. A spatial prediction device thatspatially predicts a pixel value at each pixel position within a currentblock included in an image, the device comprising: a calculation unitconfigured to calculate an integer slope based on at least one of ahorizontal gradient and a vertical gradient each of which is indicatedby a mode number, the integer slope indicating an integer value of aslope; a determining unit configured to determine a sub-pel positionthat is an intersection between (i) a line of the integer slope thatpasses through the pixel position within the current block and (ii) aboundary of a block adjacent to the current block; and a prediction unitconfigured to predict, for each of the pixel positions, the pixel valueat the pixel position based on a pixel value interpolated in the sub-pelposition determined for the pixel position.
 11. An image decodingapparatus that decodes an image coded per block, the apparatuscomprising: the spatial prediction device according to claim 10 thatpredicts a pixel value at each pixel position within a current block tobe decoded, to generate a predicted block; and an adding unit configuredto obtain a prediction error block and add the predicted block to theprediction error block.
 12. An image coding apparatus that codes animage per block, the apparatus comprising: the spatial prediction deviceaccording to claim 10 that predicts a pixel value at each pixel positionwithin a current block to be coded, to generate a predicted block; and asubtracting unit configured to subtract the predicted block from thecurrent block.
 13. A non-transitory computer-readable recording mediumon which a program for spatially predicting a pixel value at each pixelposition within a current block included in an image is recorded, theprogram causing a computer to execute: calculating an integer slopebased on at least one of a horizontal gradient and a vertical gradienteach of which is indicated by a mode number, the integer slopeindicating an integer value of a slope; determining a sub-pel positionthat is an intersection between (i) a line of the integer slope thatpasses through the pixel position within the current block and (ii) aboundary of a block adjacent to the current block; and predicting, foreach of the pixel positions, the pixel value at the pixel position basedon a pixel value interpolated in the sub-pel position determined for thepixel position.
 14. A non-transitory computer-readable recording mediumon which an image decoding program for decoding an image coded per blockis recorded, the program causing a computer to execute: predicting apixel value at each pixel position within a current block to be decoded,using the program recorded on the recording medium according to claim 13to generate a predicted block; obtaining a prediction error block; andadding the predicted block to the prediction error block.
 15. Anon-transitory computer-readable recording medium on which an imagecoding program for coding an image per block is recorded, the programcausing a computer to execute: predicting a pixel value at each pixelposition within a current block to be coded, using the program recordedon the recording medium according to claim 13 to generate a predictedblock; and subtracting the predicted block from the current block. 16.An integrated circuit that spatially predicts a pixel value at eachpixel position within a current block included in an image, the circuitcomprising: a calculation unit configured to calculate an integer slopebased on at least one of a horizontal gradient and a vertical gradienteach of which is indicated by a mode number, the integer slopeindicating an integer value of a slope; a determining unit configured todetermine a sub-pel position that is an intersection between (i) a lineof the integer slope that passes through the pixel position within thecurrent block and (ii) a boundary of a block adjacent to the currentblock; and a prediction unit configured to predict, for each of thepixel positions, the pixel value at the pixel position based on a pixelvalue interpolated in the sub-pel position determined for the pixelposition.
 17. An image decoding integrated circuit that decodes an imagecoded per block, the circuit comprising: the integrated circuitaccording to claim 16 that predicts a pixel value at each pixel positionwithin a current block to be decoded, to generate a predicted block; andan adding unit configured to obtain a prediction error block and add thepredicted block to the prediction error block.
 18. An image codingintegrated circuit that codes an image per block, the circuitcomprising: the integrated circuit according to claim 16 that predicts apixel value at each pixel position within a current block to be coded,to generate a predicted block; and a subtracting unit configured tosubtract the predicted block from the current block.